Harq feedback for multicast/unicast

ABSTRACT

In an aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may be a UE. The apparatus may receive from a second device a first data packet in one or more receiving slots of a time division duplex frame that includes a plurality of slots. The apparatus may determine whether the first data packet is received incorrectly. The apparatus may wait until the end of the one or more receiving slots and may transmit to the second device a first NACK in a NACK feedback symbol in a configured slot after the end of the one or more receiving slots in response to determining that the first data packet was not received correctly.

CROSS REFERENCE TO RELATED APPLICATION(S

This application is a Divisional of U.S. Non-provisional ApplicationSerial No. 16/578,027, entitled “HARQ FEEDBACK FOR MULTICAST/UNICAST”and filed on Sep. 20, 2019, which claims the benefit of U.S. ProvisionalApplication Serial No. 62/738,804, entitled “HARQ Feedback forMulticast/Unicast” and filed on Sep. 28, 2018, which are expresslyincorporated by reference herein in their entirety.

INTRODUCTION

The present disclosure relates generally to communication systems, andmore particularly, to methods and systems for vehicle to vehicle (V2V),Vehicle to Everything (V2X) communication, and/or other Device-to-Device(D2D) communication.

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,and broadcasts. Typical wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources. Examples of suchmultiple-access technologies include code division multiple access(CDMA) systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, orthogonal frequency divisionmultiple access (OFDMA) systems, single-carrier frequency divisionmultiple access (SC-FDMA) systems, and time division synchronous codedivision multiple access (TD-SCDMA) systems.

These multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. An example telecommunication standardis Long Term Evolution (LTE). Another example telecommunication standardis 5G New Radio (NR). 5G NR is part of a continuous mobile broadbandevolution promulgated by Third Generation Partnership Project (3GPP) tomeet new requirements associated with latency, reliability, security,scalability (e.g., with Internet of Things (IoT)), and otherrequirements. 5G NR technology may facilitate autonomous vehicles byenabling communication between vehicles (V2V), as well as other types ofvehicle communication such as vehicle to network (V2N), vehicle toinfrastructure (V2I), vehicle to pedestrian (V2P), etc., all of whichmay broadly be categorized as vehicle to everything (V2X) communication.Some aspects of 5G NR may be based on the 4G Long Term Evolution (LTE)standard. There exists a need for further improvements in V2X, V2V,and/or other D2D technology. These improvements may also be applicableto other multi-access technologies and the telecommunication standardsthat employ these technologies.

SUMMARY

The following presents a simplified summary of one or more aspects inorder to provide a basic understanding of such aspects. This summary isnot an extensive overview of all contemplated aspects, and is intendedto neither identify key or critical elements of all aspects nordelineate the scope of any or all aspects. Its sole purpose is topresent some concepts of one or more aspects in a simplified form as aprelude to the more detailed description that is presented later.

In an aspect of the disclosure, a method, a computer-readable medium,and an apparatus are provided for wireless communication by a firstdevice. In certain configurations, the apparatus may be a User Equipment(UE). The apparatus may receive from a second device a first data packetin one or more receiving slots of a time division duplex frame. Theapparatus may determine whether the first data packet is receivedincorrectly. The apparatus may wait until the end of the one or morereceiving slots and may transmit to the second device a first negativeacknowledgement signal (NACK) in a NACK feedback symbol in a slot afterthe end of the one or more receiving slots in response to determiningthat the first data packet was not received correctly.

In an aspect of the disclosure, a method, a computer-readable medium,and an apparatus are provided for wireless communication by a firstdevice. The apparatus may contend for use of one or more slots of a TimeDivision Duplex (TDD) frame for transmitting, wherein each slot of theone or more slots includes a plurality of symbols. The apparatus maytransmit at least a portion of a first packet in one or moretransmitting slots. The apparatus may reserve a first feedback symbol ofa first transmitting slot of the one or more transmitting slots forreception of a NACK from the one or more device. The apparatus mayrefrain from transmitting the first packet during the feedback symbol ofthe first transmitting slot.

In an aspect of the disclosure, a method, a computer-readable medium,and an apparatus are provided for wireless communication by a firstdevice. The apparatus receives from a second device a first data packetin one or more receiving slots of a time division duplex frame anddetermines whether the first data packet is received incorrectly. Theapparatus waits until a set of dedicated symbols to transmit a firstnegative acknowledgement signal (NACK). The apparatus transmits to thesecond device the first NACK in a NACK feedback symbol in the set ofdedicated symbols after the end of the one or more receiving slots inresponse to determining that the first data packet is receivedincorrectly.

To the accomplishment of the foregoing and related ends, the one or moreaspects comprise the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe annexed drawings set forth in detail certain illustrative featuresof the one or more aspects. These features are indicative, however, ofbut a few of the various ways in which the principles of various aspectsmay be employed, and this description is intended to include all suchaspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a wireless communicationssystem and an access network.

FIG. 2 illustrates examples of a sidelink slot structure.

FIG. 3 is a diagram illustrating an example of a base station and userequipment (UE) in an access network.

FIG. 4A, FIG. 4B, and FIG. 4C are diagrams illustrating multicasttransmission of data packets between UEs in accordance with certainaspects of the disclosure.

FIG. 5 is a diagram illustrating transmissions of NACKs for HARQ in the13^(th) symbol of a first slot after the end of transmission slots inaccordance with certain aspects of the disclosure.

FIG. 6 is a diagram illustrating transmissions of NACKs forHARQ-feedback in the second symbol of a second slot after the end oftransmission slots in accordance with certain aspects of the disclosure.

FIG. 7 is a diagram illustrating transmissions of NACKs forHARQ-feedback and turnaround time within one symbol in accordance withcertain aspects of the disclosure.

FIG. 8 is a diagram illustrating transmissions of NACKs forHARQ-feedback in dedicated NACK symbols after every N slots inaccordance with certain aspects of the disclosure.

FIG. 9A and FIG. 9B are diagrams illustrating transmissions of NACKs forHARQ-feedback in dedicated NACK symbols after every 3 slots inaccordance with certain aspects of the disclosure.

FIG. 10 illustrates feedback channels containing NACKs for multicast andunicast transmissions in accordance with certain aspects of thedisclosure.

FIG. 11 is a call flow diagram illustrating an implementation of datapacket transmissions from a transmitting UE and NACKs for HARQ-feedbackfrom a receiving UE in accordance with certain aspects of thedisclosure.

FIG. 12 is a flowchart of a method for receiving data packets from atransmitting UE and transmitting NACK feedbacks that may be implementedby a receiving UE in accordance with certain aspects of the disclosure.

FIG. 13 is a conceptual data flow diagram illustrating the data flowbetween different modules/means/components in an example apparatus of areceiving UE in accordance with certain aspects of the disclosure.

FIG. 14 is a diagram illustrating an example of a hardwareimplementation for an apparatus of a receiving UE employing a processingsystem in accordance with certain aspects of the disclosure.

FIG. 15 is a flowchart of a method for transmitting multicast datapackets and receiving NACK feedbacks from a receiving UE that may beimplemented by a transmitting UE in accordance with certain aspects ofthe disclosure.

FIG. 16 is a conceptual data flow diagram illustrating the data flowbetween different modules/means/components in an example apparatus of atransmitting UE in accordance with certain aspects of the disclosure.

FIG. 17 is a diagram illustrating an example of a hardwareimplementation for an apparatus of a transmitting UE employing aprocessing system in accordance with certain aspects of the disclosure.

FIG. 18 is a flowchart of a method of wireless communication thatinvolves receiving data packets from a transmitting UE and transmittingfeedback that may be implemented by a receiving UE in accordance withcertain aspects of the disclosure.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. In some instances, well known structures and components areshown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented withreference to various apparatus and methods. These apparatus and methodswill be described in the following detailed description and illustratedin the accompanying drawings by various blocks, components, circuits,processes, algorithms, etc. (collectively referred to as “elements”).These elements may be implemented using electronic hardware, computersoftware, or any combination thereof. Whether such elements areimplemented as hardware or software depends upon the particularapplication and design constraints imposed on the overall system.

By way of example, an element, or any portion of an element, or anycombination of elements may be implemented as a “processing system” thatincludes one or more processors. Examples of processors includemicroprocessors, microcontrollers, graphics processing units (GPUs),central processing units (CPUs), application processors, digital signalprocessors (DSPs), reduced instruction set computing (RISC) processors,systems on a chip (SoC), baseband processors, field programmable gatearrays (FPGAs), programmable logic devices (PLDs), state machines, gatedlogic, discrete hardware circuits, and other suitable hardwareconfigured to perform the various functionality described throughoutthis disclosure. One or more processors in the processing system mayexecute software. Software shall be construed broadly to meaninstructions, instruction sets, code, code segments, program code,programs, subprograms, software components, applications, softwareapplications, software packages, routines, subroutines, objects,executables, threads of execution, procedures, functions, etc., whetherreferred to as software, firmware, middleware, microcode, hardwaredescription language, or otherwise.

Accordingly, in one or more example embodiments, the functions describedmay be implemented in hardware, software, or any combination thereof. Ifimplemented in software, the functions may be stored on or encoded asone or more instructions or code on a computer-readable medium.Computer-readable media includes computer storage media. Storage mediamay be any available media that can be accessed by a computer. By way ofexample, and not limitation, such computer-readable media can comprise arandom-access memory (RAM), a read-only memory (ROM), an electricallyerasable programmable ROM (EEPROM), optical disk storage, magnetic diskstorage, other magnetic storage devices, combinations of theaforementioned types of computer-readable media, or any other mediumthat can be used to store computer executable code in the form ofinstructions or data structures that can be accessed by a computer.

FIG. 1 is a diagram illustrating an example of a wireless communicationssystem and an access network 100. The wireless communications system(also referred to as a wireless wide area network (WWAN)) includes basestations 102, UEs 104, an Evolved Packet Core (EPC) 160, and a CoreNetwork (e.g., 5GC) 190. The base stations 102 may include macro cells(high power cellular base station) and/or small cells (low powercellular base station). The macro cells include base stations. The smallcells include femtocells, picocells, and microcells.

The base stations 102 configured for 4G LTE (collectively referred to asEvolved Universal Mobile Telecommunications System (UMTS) TerrestrialRadio Access Network (E-UTRAN)) may interface with the EPC 160 throughbackhaul links 132 (e.g., S1 interface). The base stations 102configured for NR (collectively referred to as Next Generation RAN(NG-RAN)) may interface with Core Network 190 through backhaul links184. In addition to other functions, the base stations 102 may performone or more of the following functions: transfer of user data, radiochannel ciphering and deciphering, integrity protection, headercompression, mobility control functions (e.g., handover, dualconnectivity), inter-cell interference coordination, connection setupand release, load balancing, distribution for non-access stratum (NAS)messages, NAS node selection, synchronization, radio access network(RAN) sharing, multimedia broadcast multicast service (MBMS), subscriberand equipment trace, RAN information management (RIM), paging,positioning, and delivery of warning messages. The base stations 102 maycommunicate directly or indirectly (e.g., through the EPC 160 or CoreNetwork 190) with each other over backhaul links 134 (e.g., X2interface). The backhaul links 134 may be wired or wireless.

The base stations 102 may wirelessly communicate with the UEs 104. Eachof the base stations 102 may provide communication coverage for arespective geographic coverage area 110. There may be overlappinggeographic coverage areas 110. For example, the small cell 102′ may havea coverage area 110′ that overlaps the coverage area 110 of one or morebase stations 102, such as macro base station. A network that includesboth small cell and macro cells may be known as a heterogeneous network.A heterogeneous network may also include Home Evolved Node Bs (eNBs)(HeNBs), which may provide service to a restricted group known as aclosed subscriber group (CSG). The communication links 120 between thebase stations 102 and the UEs 104 may include uplink (UL) (also referredto as reverse link) transmissions from a UE 104 to a base station 102and/or downlink (DL) (also referred to as forward link) transmissionsfrom a base station 102 to a UE 104. The communication links 120 may usemultiple-input and multiple-output (MIMO) antenna technology, includingspatial multiplexing, beamforming, and/or transmit diversity. Thecommunication links may be through one or more carriers. The basestations 102 / UEs 104 may use spectrum up to Y MHz (e.g., 5, 10, 15,20, 100, 400, etc. MHz) bandwidth per carrier allocated in a carrieraggregation of up to a total of Yx MHz (x component carriers) used fortransmission in each direction. The carriers may or may not be adjacentto each other. Allocation of carriers may be asymmetric with respect toDL and UL (e.g., more or less carriers may be allocated for DL than forUL). The component carriers may include a primary component carrier andone or more secondary component carriers. A primary component carriermay be referred to as a primary cell (PCell) and a secondary componentcarrier may be referred to as a secondary cell (SCell).

Certain UEs 104 may communicate with each other using device-to-device(D2D) communication link 158. The D2D communication link 158 may use theDL/UL WWAN spectrum. The D2D communication link 158 may use one or moresidelink channels, such as a physical sidelink broadcast channel(PSBCH), a physical sidelink discovery channel (PSDCH), a physicalsidelink shared channel (PSSCH), and a physical sidelink control channel(PSCCH). D2D communication may be through a variety of wireless D2Dcommunications systems, such as for example, FlashLinQ, WiMedia,Bluetooth, ZigBee, Wi-Fi based on the IEEE 802.11 standard, LTE, or NR.

The wireless communications system may further include a Wi-Fi accesspoint (AP) 150 in communication with Wi-Fi stations (STAs) 152 viacommunication links 154 in a 5 GHz unlicensed frequency spectrum. Whencommunicating in an unlicensed frequency spectrum, the STAs 152 / AP 150may perform a clear channel assessment (CCA) prior to communicating inorder to determine whether the channel is available.

The small cell 102′ may operate in a licensed and/or an unlicensedfrequency spectrum. When operating in an unlicensed frequency spectrum,the small cell 102′ may employ NR and use the same 5 GHz unlicensedfrequency spectrum as used by the Wi-Fi AP 150. The small cell 102′,employing NR in an unlicensed frequency spectrum, may boost coverage toand/or increase capacity of the access network.

A base station 102, whether a small cell 102′ or a large cell (e.g.,macro base station), may include an eNB, gNodeB (gNB), or other type ofbase station. Some base stations 180, such as a gNB, may operate in atraditional sub 6 GHz spectrum, in millimeter wave (mmW) frequencies,and/or near mmW frequencies in communication with the UE 104. When thebase station 180 operates in mmW or near mmW frequencies, the basestation 180 may be referred to as an mmW base station. Extremely highfrequency (EHF) is part of the RF in the electromagnetic spectrum. EHFhas a range of 30 GHz to 300 GHz and a wavelength between 1 millimeterand 10 millimeters. Radio waves in the band may be referred to as amillimeter wave. Near mmW may extend down to a frequency of 3 GHz with awavelength of 100 millimeters. The super high frequency (SHF) bandextends between 3 GHz and 30 GHz, also referred to as centimeter wave.Communications using the mmW / near mmW radio frequency band hasextremely high path loss and a short range. A mmW base station, such asbase station 180, may utilize beamforming 182 with the UE 104 tocompensate for the extremely high path loss and short range.

Devices may use beamforming to transmit and receive communication. Forexample, FIG. 1 illustrates that a base station 180 may transmit abeamformed signal to the UE 104 in one or more transmit directions 182′.The UE 104 may receive the beamformed signal from the base station 180in one or more receive directions 182″. The UE 104 may also transmit abeamformed signal to the base station 180 in one or more transmitdirections. The base station 180 may receive the beamformed signal fromthe UE 104 in one or more receive directions. The base station 180 / UE104 may perform beam training to determine the best receive and transmitdirections for each of the base station 180 / UE 104. The transmit andreceive directions for the base station 180 may or may not be the same.The transmit and receive directions for the UE 104 may or may not be thesame. Although beamformed signals are illustrated between UE 104 andbase station 102/180, aspects of beamforming may similarly may beapplied by UE 104 or RSU 107 to communicate with another UE 104 or RSU107, such as based on V2X, V2V, or other D2D communication.

The EPC 160 may include a Mobility Management Entity (MME) 162, otherMMEs 164, a Serving Gateway 166, a Multimedia Broadcast MulticastService (MBMS) Gateway 168, a Broadcast Multicast Service Center (BM-SC)170, and a Packet Data Network (PDN) Gateway 172. The MME 162 may be incommunication with a Home Subscriber Server (HSS) 174. The MME 162 isthe control node that processes the signaling between the UEs 104 andthe EPC 160. Generally, the MME 162 provides bearer and connectionmanagement. All user Internet protocol (IP) packets are transferredthrough the Serving Gateway 166, which itself is connected to the PDNGateway 172. The PDN Gateway 172 provides UE IP address allocation aswell as other functions. The PDN Gateway 172 and the BM-SC 170 areconnected to the IP Services 176. The IP Services 176 may include theInternet, an intranet, an IP Multimedia Subsystem (IMS), a PS StreamingService, and/or other IP services. The BM-SC 170 may provide functionsfor MBMS user service provisioning and delivery. The BM-SC 170 may serveas an entry point for content provider MBMS transmission, may be used toauthorize and initiate MBMS Bearer Services within a public land mobilenetwork (PLMN), and may be used to schedule MBMS transmissions. The MBMSGateway 168 may be used to distribute MBMS traffic to the base stations102 belonging to a Multicast Broadcast Single Frequency Network (MBSFN)area broadcasting a particular service, and may be responsible forsession management (start/stop) and for collecting eMBMS relatedcharging information.

The Core Network 190 may include a Access and Mobility ManagementFunction (AMF) 192, other AMFs 193, a Session Management Function (SMF)194, and a User Plane Function (UPF) 195. The AMF 192 may be incommunication with a Unified Data Management (UDM) 196. The AMF 192 isthe control node that processes the signaling between the UEs 104 andthe Core Network 190. Generally, the AMF 192 provides QoS flow andsession management. All user Internet protocol (IP) packets aretransferred through the UPF 195. The UPF 195 provides UE IP addressallocation as well as other functions. The UPF 195 is connected to theIP Services 197. The IP Services 197 may include the Internet, anintranet, an IP Multimedia Subsystem (IMS), a PS Streaming Service,and/or other IP services.

The base station may also be referred to as a gNB, Node B, evolved NodeB (eNB), an access point, a base transceiver station, a radio basestation, a radio transceiver, a transceiver function, a basic serviceset (BSS), an extended service set (ESS), a transmit reception point(TRP), or some other suitable terminology. The base station 102 providesan access point to the EPC 160 or Core Network 190 for a UE 104.Examples of UEs 104 include a cellular phone, a smart phone, a sessioninitiation protocol (SIP) phone, a laptop, a personal digital assistant(PDA), a satellite radio, a global positioning system, a multimediadevice, a video device, a digital audio player (e.g., MP3 player), acamera, a game console, a tablet, a smart device, a wearable device, avehicle, an electric meter, a gas pump, a large or small kitchenappliance, a healthcare device, an implant, a sensor/actuator, adisplay, or any other similar functioning device. Some of the UEs 104may be referred to as IoT devices (e.g., parking meter, gas pump,toaster, vehicles, heart monitor, etc.). The UE 104 may also be referredto as a station, a mobile station, a subscriber station, a mobile unit,a subscriber unit, a wireless unit, a remote unit, a mobile device, awireless device, a wireless communications device, a remote device, amobile subscriber station, an access terminal, a mobile terminal, awireless terminal, a remote terminal, a handset, a user agent, a mobileclient, a client, or some other suitable terminology.

Some wireless communication networks may include vehicle-basedcommunication devices that can communicate from vehicle-to-vehicle(V2V), vehicle-to-infrastructure (V2I) (e.g., from the vehicle-basedcommunication device to road infrastructure nodes such as a Road SideUnit (RSU)), vehicle-to-network (V2N) (e.g., from the vehicle-basedcommunication device to one or more network nodes, such as a basestation), and/or a combination thereof and/or with other devices, whichcan be collectively referred to as vehicle-to-anything (V2X)communications. Referring again to FIG. 1 , in certain aspects, a UE104, e.g., a transmitting Vehicle User Equipment (VUE) or other UE, maybe configured to transmit messages directly to another UE 104. Thecommunication may be based on V2V/V2X/V2I or other D2D communication,such as Proximity Services (ProSe), etc. Communication based on V2V,V2X, V2I, and/or other D2D may also be transmitted and received by othertransmitting and receiving devices, such as Road Side Unit (RSU) 107,etc. Aspects of the communication may be based on PC5 or sidelinkcommunication e.g., as described in connection with the example in FIG.2 . Although the following description may provide examples for V2X/D2Dcommunication in connection with 5G NR, the concepts described hereinmay be applicable to other similar areas, such as LTE, LTE-A, CDMA, GSM,and other wireless technologies.

In certain aspects, a UE 104 may receive from a second device a firstdata packet in one or more receiving slots of a time division duplexframe that includes a plurality of slots. The apparatus may determinewhether the first data packet is received incorrectly. The apparatus mayinclude a feedback component 198 that is configured to wait until theend of the one or more receiving slots before transmitting a NACK in aNACK feedback symbol in a configured slot in response to determiningthat the first data packet was not received correctly.

In other aspects, UE 104 may contend for use of one or more slots of aplurality of slots of a TDD frame for transmitting, wherein each slotincludes a plurality of symbols. The apparatus may transmit a firstpacket to one or more devices in one or more transmitting slots. Theapparatus may include a reservation component 199 configured to reservea feedback symbol of a transmitting slot of the one or more transmittingslots for feedback from the one or more devices. The apparatus mayrefrain from transmitting the first packet during the feedback symbol ofthe transmitting slot.

FIG. 2 illustrates example diagrams 200 and 210 illustrating examplesslot structures that may be used for wireless communication between UE104 and UE 104′, e.g., for sidelink communication. The slot structuremay be within a 5G/NR frame structure. Although the followingdescription may be focused on 5G NR, the concepts described herein maybe applicable to other similar areas, such as LTE, LTE-A, CDMA, GSM, andother wireless technologies. This is merely one example, and otherwireless communication technologies may have a different frame structureand/or different channels. A frame (10 ms) may be divided into 10equally sized subframes (1 ms). Each subframe may include one or moretime slots. Subframes may also include mini-slots, which may include 7,4, or 2 symbols. Each slot may include 7 or 14 symbols, depending on theslot configuration. For slot configuration 0, each slot may include 14symbols, and for slot configuration 1, each slot may include 7 symbols.Diagram 200 illustrates a single slot transmission, e.g., which maycorrespond to a 0.5 ms transmission time interval (TTI). Diagram 210illustrates an example two-slot aggregation, e.g., an aggregation of two0.5 ms TTIs. Diagram 200 illustrates a single RB, whereas diagram 210illustrates N RBs. In diagram 210, 10 RBs being used for control ismerely one example. The number of RBs may differ.

A resource grid may be used to represent the frame structure. Each timeslot may include a resource block (RB) (also referred to as physical RBs(PRBs)) that extends 12 consecutive subcarriers. The resource grid isdivided into multiple resource elements (REs). The number of bitscarried by each RE depends on the modulation scheme. As illustrated inFIG. 2 , some of the REs may comprise control information, e.g., alongwith demodulation RS (DMRS). FIG. 2 also illustrates that symbol(s) maycomprise CSI-RS. The symbols in FIG. 2 that are indicated for DMRS orCSI-RS indicate that the symbol comprises DMRS or CSI-RS REs. Suchsymbols may also comprise REs that include data. For example, if anumber of ports for DMRS or CSI-RS is 1 and a comb-2 pattern is used forDMRS/CSI-RS, then half of the REs may comprise the RS and the other halfof the REs may comprise data. A CSI-RS resource may start at any symbolof a slot, and may occupy 1, 2, or 4 symbols depending on a configurednumber of ports. CSI-RS can be periodic, semi-persistent, or aperiodic(e.g., based on DCI triggering). For time/frequency tracking, CSI-RS maybe either periodic or aperiodic. CSI-RS may be transmitted in busts oftwo or four symbols that are spread across one or two slots. The controlinformation may comprise Sidelink Control Information (SCI). At leastone symbol may be used for feedback, as described herein. A symbol priorto and/or after the feedback may be used for turnaround betweenreception of data and transmission of the feedback. Although symbol 12is illustrated for data, it may instead be a gap symbol to enableturnaround for feedback in symbol 13. Another symbol, e.g., at the endof the slot may be used as a gap. The gap enables a device to switchfrom operating as a transmitting device to prepare to operate as areceiving device, e.g., in the following slot. Data may be transmittedin the remaining REs, as illustrated. The data may comprise the datamessage described herein. The position of any of the SCI, feedback, andLBT symbols may be different than the example illustrated in FIG. 2 .Multiple slots may be aggregated together. FIG. 2 also illustrates anexample aggregation of two slot. The aggregated number of slots may alsobe larger than two. When slots are aggregated, the symbols used forfeedback and/or a gap symbol may be different that for a single slot.While feedback is not illustrated for the aggregated example, symbol(s)in a multiple slot aggregation may also be allocated for feedback, asillustrated in the one slot example.

FIG. 3 is a block diagram of a first wireless communication device 310in communication with a second wireless communication device 350, e.g.,via V2V/V2X/D2D communication. The device 310 may comprise atransmitting device communicating with a receiving device, e.g., device350, via V2V/V2X/D2D communication. The communication may be based,e.g., on sidelink. The device 310 may comprise a UE, an RSU, etc. Thereceiving device may comprise a UE, an RSU, etc. Packets may be providedto a controller/processor 375 that implements layer 3 and layer 2functionality. Layer 3 includes a radio resource control (RRC) layer,and layer 2 includes a packet data convergence protocol (PDCP) layer, aradio link control (RLC) layer, and a medium access control (MAC) layer.

The transmit (TX) processor 316 and the receive (RX) processor 370implement layer 1 functionality associated with various signalprocessing functions. Layer 1, which includes a physical (PHY) layer,may include error detection on the transport channels, forward errorcorrection (FEC) coding/decoding of the transport channels,interleaving, rate matching, mapping onto physical channels,modulation/demodulation of physical channels, and MIMO antennaprocessing. The TX processor 316 handles mapping to signalconstellations based on various modulation schemes (e.g., binaryphase-shift keying (BPSK), quadrature phase-shift keying (QPSK),M-phase-shift keying (M-PSK), M-quadrature amplitude modulation(M-QAM)). The coded and modulated symbols may then be split intoparallel streams. Each stream may then be mapped to an OFDM subcarrier,multiplexed with a reference signal (e.g., pilot) in the time and/orfrequency domain, and then combined together using an Inverse FastFourier Transform (IFFT) to produce a physical channel carrying a timedomain OFDM symbol stream. The OFDM stream is spatially precoded toproduce multiple spatial streams. Channel estimates from a channelestimator 374 may be used to determine the coding and modulation scheme,as well as for spatial processing. The channel estimate may be derivedfrom a reference signal and/or channel condition feedback transmitted bythe device 350. Each spatial stream may then be provided to a differentantenna 320 via a separate transmitter 318TX. Each transmitter 318TX maymodulate an RF carrier with a respective spatial stream fortransmission.

At the device 350, each receiver 354RX receives a signal through itsrespective antenna 352. Each receiver 354RX recovers informationmodulated onto an RF carrier and provides the information to the receive(RX) processor 356. The TX processor 368 and the RX processor 356implement layer 1 functionality associated with various signalprocessing functions. The RX processor 356 may perform spatialprocessing on the information to recover any spatial streams destinedfor the device 350. If multiple spatial streams are destined for thedevice 350, they may be combined by the RX processor 356 into a singleOFDM symbol stream. The RX processor 356 then converts the OFDM symbolstream from the time-domain to the frequency domain using a Fast FourierTransform (FFT). The frequency domain signal comprises a separate OFDMsymbol stream for each subcarrier of the OFDM signal. The symbols oneach subcarrier, and the reference signal, are recovered and demodulatedby determining the most likely signal constellation points transmittedby device 310. These soft decisions may be based on channel estimatescomputed by the channel estimator 358. The soft decisions are thendecoded and deinterleaved to recover the data and control signals thatwere originally transmitted by device 310 on the physical channel. Thedata and control signals are then provided to the controller/processor359, which implements layer 3 and layer 2 functionality.

The controller/processor 359 can be associated with a memory 360 thatstores program codes and data. The memory 360 may be referred to as acomputer-readable medium. The controller/processor 359 may providedemultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, and control signalprocessing. The controller/processor 359 is also responsible for errordetection using an ACK and/or NACK protocol to support HARQ operations.

Similar to the functionality described in connection with thetransmission by device 310, the controller/processor 359 may provide RRClayer functionality associated with system information (e.g., MIB, SIBs)acquisition, RRC connections, and measurement reporting; PDCP layerfunctionality associated with header compression / decompression, andsecurity (ciphering, deciphering, integrity protection, integrityverification); RLC layer functionality associated with the transfer ofupper layer PDUs, error correction through ARQ, concatenation,segmentation, and reassembly of RLC SDUs, re-segmentation of RLC dataPDUs, and reordering of RLC data PDUs; and MAC layer functionalityassociated with mapping between logical channels and transport channels,multiplexing of MAC SDUs onto TBs, demultiplexing of MAC SDUs from TBs,scheduling information reporting, error correction through HARQ,priority handling, and logical channel prioritization.

Channel estimates derived by a channel estimator 358 from a referencesignal or feedback transmitted by device 310 may be used by the TXprocessor 368 to select the appropriate coding and modulation schemes,and to facilitate spatial processing. The spatial streams generated bythe TX processor 368 may be provided to different antenna 352 viaseparate transmitters 354TX. Each transmitter 354TX may modulate an RFcarrier with a respective spatial stream for transmission.

The transmission is processed at the device 310 in a manner similar tothat described in connection with the receiver function at the device350. Each receiver 318RX receives a signal through its respectiveantenna 320. Each receiver 318RX recovers information modulated onto anRF carrier and provides the information to a RX processor 370.

The controller/processor 375 can be associated with a memory 376 thatstores program codes and data. The memory 376 may be referred to as acomputer-readable medium. The controller/processor 375 providesdemultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signalprocessing. The controller/processor 375 is also responsible for errordetection using an ACK and/or NACK protocol to support HARQ operations.

At least one of the TX processor 368, the RX processor 356, or thecontroller/processor 359 of device 350 or the TX 316, the RX processor370, or the controller/processor 375 may be configured to performaspects described in connection with 198 and/or 199 of FIG. 1 .

FIGS. 4A, 4B, and 4C are diagrams illustrating multicast transmission ofdata packets between UEs in accordance with certain aspects of thedisclosure. V2V/V2X/D2D communication may be implemented in adecentralized manner without relying on a base station to coordinate thecommunication. Each UE may contend for transmission resources and maytake turns assuming the role of a transmitting UE during one or moreslots and receiving during other slots. For example, in FIG. 4A, a firstUE 410 may acquire the transmission resources for one or more slots totransmit its sensor data as a data packet in a multicast transmission411 to a second UE 420 and a third UE 430. A second UE 420 or a third UE430 may decode the data packet and if the data packet is not decodedcorrectly (e.g., fails a cyclic redundancy check (CRC)), second UE 420or third UE 430 may transmit a NACK feedback to first UE 410. Second UE420 or third UE 430 may transmit the NACK after the slots during whichthe data packet was received.

FIG. 4B illustrates a scenario in which second UE 420 contends andacquires the transmission resources for one or more slots to transmitits sensor data as a data packet in a multicast transmission 421 afterfirst UE 410 has finished its transmission. If third UE 430 did notcorrectly decode the data packet from the first UE 410 during themulticast transmission 411 of FIG. 4A, the third UE 430 may transmit aNACK 422 to the first UE 410 in the slots during which the multicasttransmission 421 is received from the second UE 420. In one aspect, afeedback symbol in a slot of the one or more slots used by the second UE420 for the multicast transmission 421 may be reserved for any UEs totransmit a NACK. During the feedback symbol, the second UE 420 mayrefrain from transmitting the multicast transmission 421. The third UE430 may use this reserved feedback symbol to transmit the NACK 422 tothe first UE 410. In one aspect, the third UE may transmit the NACK 422as a broadcast packet. The third UE 430 may switch from a receiving modeto a transmitting mode to transmit the NACK 422 using the reservedfeedback symbol. The third UE 430 may then switch from the transmittingmode back to the receiving mode to resume receiving the multicasttransmission 421 from the second UE 420. During the switching betweenthe receiving and transmitting modes, the third UE 430 may puncture datareceived from the multicast transmission 421. The first UE 410 mayreceive the NACK 422 in the reserved feedback symbol indicating that thethird UE 430 did not receive correctly the data packet transmittedduring the multicast transmission 411. The first UE 410 may retransmitits data packet by contending for the transmission resources after thesecond UE completes its multicast transmission 421.

FIG. 4C illustrates a second scenario in which the second UE 420contends and acquires the transmission resources for one or more slotsfor the multicast transmission 421 of its data packet after the first UE410 has finished its transmission. In this scenario, the second UE 420did not decode correctly the data packet transmitted from the first UE410 during the multicast transmission 411 of FIG. 4A. The second UE 420may use the reserved feedback symbol during its multicast transmission421 to transmit a NACK to the first UE 410. Because the second UE 420 isalready the transmitting UE, the second UE 420 need not switch betweenthe receiving and transmitting modes. After transmitting the NACK usingthe reserved feedback symbol, the second UE 420 may resume transmittingits data packet for the remainder of its one or more slots. The first UE410, upon receiving the NACK, may retransmit its data packet bycontending for the transmission resources after the second UE completesits multicast transmission 421.

FIGS. 4A, 4B, and 4C illustrate certain aspects of the disclosure usingmulticast transmission of data packets between UEs in V2V, V2X, or otherD2D communication, e.g., using unicast, multicast, broadcast, or otherprotocols. While the examples illustrate communication between UEs, theaspects presented herein may also be performed by other types of UEs, aRoad Side Unit (RSU), or base station engaged in V2V, V2X, and/or otherD2D communication.

FIG. 5 illustrates an example link level design for TDD communication inwhich a device does not transmit and receive at the same time. A slotmay comprise 14 symbols, as illustrated in FIG. 5 . Communication may beperformed based on one slot or an aggregation of multiple slots in thelink level design.

FIG. 5 is a diagram illustrating transmissions of NACKs for HARQ in the13^(th) symbol of a first slot following the end of a transmission(e.g., a first transmit slot following a previous transmission) inaccordance with certain aspects of the disclosure. Although FIG. 5illustrates a feedback symbol that occurs in the 13^(th) symbol, itshould be understood that other symbols may be used and that the 13^(th)symbol is merely one example location for the feedback symbol.Transmission resources are shown as resource blocks that include 12carriers in the vertical direction representing frequency and 14 symbolsin the horizontal direction representing time. The 14 symbols, labeledas symbols 1-14, may constitute a slot. The number of symbols in a slotmay vary. For example, slots with an extended cyclic prefix or othervariation may have a different number of symbols. A transmitting devicemay acquire one or more slots for transmission of a transport block,e.g., based on V2V/V2X/D2D. In one aspect, a transport block maycomprise a data packet.

In the four slots depicted in timeline 510, a UE may be in atransmitting mode for a two slot aggregation followed by a slot duringwhich the UE is in the receiving mode, which may then be followed by aslot during which the UE is in the transmitting mode, again. The UE maycorrespond to any of the UEs illustrated in FIGS. 4A-4C. For example, iffirst UE 410 has a data packet to transmit, first UE 410 may contend foraccess to transmission resources by transmitting a listen-before-talk(LBT) sequence 520 during symbol 1 of the first slot. Other UEs maycontend for the transmission resources by transmitting their LBTsequences in other symbols. For a packet transmission based on LBTcounter 0, the LBT may be transmitted in the first symbol of the slot.For a packet transmission based on LBT counter 1, the transmitter maywait until the third symbol to transmit the LBT, e.g., as illustrated intimeline 514. The transmitting device may select, e.g., randomly betweendifferent LBT counters for each packet transmission. Thus, symbol 3 of aslot may be deemed a vulnerable symbol 522 that may be vulnerable to LBTsequences transmitted by other contending UEs using LBT counter 1. Whenfirst UE 410 utilizes the transmission resources, first UE 410 may useone or more slots for transmitting data, control, and RS. For example,as shown in FIG. 5 , first UE 410 may transmit control information,reference signals, and/or a data packet in the aggregation of twotransmitting slots that includes the first and the second slot.

Symbol 13 of the first slot of the two slot aggregation may be reservedas a NACK feedback symbol 526 for use by UE(s) for transmitting a NACKin response to the UE(s) not being able to correctly decode a datapacket received in a previous transmission. For example, if second UE420 could not correctly decode a data packet received from first UE 410,or from any other transmitting UE, during an aggregation of one or moretransmitting slots that precedes the current two slot aggregation inslots 1 and 2, second UE 420 may transmit a NACK during the NACKfeedback symbol 526 in symbol 13 of the first slot of the current twoslot aggregation. The corresponding slots for the second UE may beillustrated by the timeline of 512. Similarly, if third UE 430 could notcorrectly decode the data packet received from first UE 410, or anyother transmitting UE, for the transmission that precedes the currenttwo slot aggregation, third UE 430 may also transmit a NACK feedbacksymbol 526 during the NACK feedback symbol 526 in the first slot of thecurrent two slot aggregation.

In another scenario, a third UE 430 may be transmitting in the same slotor slots as the first UE 410, but using a different frequency from thetransmitting frequency used by the first UE 410. The slots for the thirdUE may be illustrated by timeline 514. The third UE 430 may reservesymbol 13 as a NACK feedback symbol for NACK transmission by other UEs,as in UE 410. One or more devices may transmit NACKs on the same NACKfeedback symbol. While the third UE 430 may receive NACKs in symbol 13of the first slot on a different frequency from that used by the firstUE 410 to receive NACKs, there may be interference between transmissionsof the NACK feedback symbols on the two frequencies. This is because ofincreased power leakage when multiple UEs transmit NACKs on the samefrequency. For the third UE 430, symbol 13 of the first slot is shown asa symbol vulnerable to NACK because of possible interference from theNACK transmitted by the UE 420 on a different frequency in the firstslot of the two slot aggregation of the UE 410.

As mentioned, in the timeline 512, a receiving UE such as the second UE420 may transmit a NACK in the NACK feedback symbol 526. The second UE420 may receive the transmission from the first UE 410 during symbols4-11 of the first slot of the two slot aggregation used by the first UE410 for transmitting. At symbol 12, one symbol before the NACK feedbacksymbol 526, the second UE 420 may switch from the receiving mode to thetransmitting mode using a gap symbol 530. During symbol 12, alsoreferred to as the first turnaround symbol, the first UE 410 maycontinue to transmit its data packet. In one aspect, the first UE 410may fill symbols 12 with residual data after performing code ratematching of the data to be transmitted so that the code rate matcheddata is filled in symbol 12, and also in symbol 14 as will be discussed,after other symbols (e.g., symbols 2, 4-11) carrying the data packet arefilled.

In one aspect, the first UE 410 may elect not to transmit on symbols 12and 14 by performing code rate matching of the data to be transmitted sothat only symbols 2 and 4-11 are filled with the data packet. In thisscenario, the turnaround symbols used by the UEs transmitting the NACKto transition from the receiving mode to the transmitting mode and thenback to the receiving mode may be referred to as punctured symbols atthe UE transmitting data packets. As shown in FIG. 5 , symbol 12 of thefirst transmitting slot for the first UE 410 and for the third UE 430are shown as a punctured symbol 524 because the first UE 410 and thethird UE 430 do not transmit their data packets during symbol 12.

During the NACK feedback symbol 526, the first UE 410 refrains fromtransmitting. The NACK transmitted from the second UE 420 may bereceived by the first UE 410 to indicate that data packet transmitted ina transmission prior to the current two slot aggregation was notcorrectly decoded by the second UE 420 if the prior transmission wasfrom the first UE 410. The first UE 410 may contend for transmissionresources following the current two slot aggregation to retransmit thedata packet that was not successfully decoded by the second UE 420 in alater transmission. In one aspect, if the transmission prior to thecurrent two slot aggregation was from another UE, and if the first UE410 did not correctly decode the data packet transmitted in the priortransmission, the first UE 410 may transmit a NACK using the NACKfeedback symbol 526 to request retransmission from the UE transmittingin the prior transmission.

At symbol 14 of the first slot of the two slot aggregation, one symbolafter the NACK feedback symbol 526, the second UE 420 may switch fromthe transmitting mode back to the receiving mode using another gapsymbol 530. In one aspect, during symbol 14, also referred to as thesecond turnaround symbol, first UE may resume transmitting its datapacket. This is because other UEs that do not transmit NACKs during theNACK feedback symbol 526 may continue to receive the data packet fromfirst UE 410 during symbols 12 and 14. To accommodate NACK transmittingUEs, such as UE 420, without compromising the data rate of other UEsthat do not transmit NACKs in a slot, first UE 410 may fill symbols 12and 14 in every slot after all other symbols in the aggregation oftransmitting slots are filled with code rate matched data from a buffer.That is, the data packet may not be transmitted in the order of thesymbols in the slot. Instead, residual data following code rate matchingmay be filled in symbols 12 and 14 after the remaining data carryingsymbols (e.g., symbols 2, 4-11) in the slot are filled. This may allowfor improved efficiency for those devices that are not transmitting NACKfeedback.

In the second slot of the two slot aggregation, symbols 1 and 3 may bevulnerable symbols 522 that are vulnerable to LBT sequences transmittedby UEs wishing to gain access to the transmission resources. Becausefirst UE 410 is transmitting for the two slot aggregation, first UE maycontinue to transmit the data packet during symbols 2 and 4-11 of thesecond slot. First UE 410 may also transmit the data packet duringsymbols 12 and 13. As with symbol 12 in the first slot of the two slotaggregation, symbol 12 in the second slot may be filled with residualdata following code rate matching after the symbols 2 and 4-11 of in thetwo transmitting slots are filled. Unlike symbols 13 in the first slotof the two slot aggregation, first UE 410 may use symbol 13 in thesecond slot to transmit the data packet because first UE 410 does notexpect to receive a NACK feedback symbol in the second slot of the twoslot aggregation. However, symbol 13 of the second slot may be a symbol528 vulnerable to NACK transmission from other devices, such as UEstransmitting NACKs on a different frequency. For example, during thesecond slot, second UE 420 may transmit a NACK in symbol 13 on adifferent frequency to respond to the data packet transmitted by thirdUE 430 in the one slot transmission using the first slot. During symbol14 of the second transmitting slot of the two slot aggregation, first UE410 may transition from the transmitting mode to a receiving mode byusing a gap symbol 530.

At slot 3, after first UE 410 has completed transmitting, UEs maycontend for access to the transmission resources by transmitting a LBTsequence 520 during symbol 1 and during symbol 3. For example, asdepicted in timeline 514, third UE 430 may transmit an LBT sequence 520during the third symbol for LBT counter 1 to contend for access to thetransmission resources. If third UE 430 utilizes the transmissionresources, third UE 430 may use one or more slots for transmitting. Forexample, third UE 430 may transmit control information, referencesignals, and a data packet using slot 3 in a one slot transmission.

Third UE 430 may reserve symbol 13 of its first transmission slot (alsoits lone transmission slot) for use by any UEs for transmitting a NACK.Third UE 430 may receive the NACK on a different frequency than thefrequency used by first UE 410 to receive its NACK. For example, asdepicted in timeline 512, if second UE 420 could not correctly decodethe data packet transmitted from UE 410 during the previous two slotaggregation, second UE 420 may transmit a NACK during the NACK feedbacksymbol 526 of the slot 3 to first UE 410 on a different frequency fromthe frequency used by third UE 430 to receive its NACK. During symbols4-11 of the slot 3, second UE 420 may receive transmission from otherUEs. At symbol 12, second UE 420 may switch from the receiving mode tothe transmitting mode using a gap symbol 530 to prepare for transmittingthe NACK.

During symbol 13 of slot 3, third UE may refrain from transmitting. TheNACK transmitted from second UE 420 may be received by first UE 410 toindicate that the data packet transmitted during the previous two slotaggregation was not correctly decoded by second UE 420. First UE 410 maycontend for transmission resources following the one slot transmissionby third UE 430 to retransmit the data packet. Any NACKs received bythird UE 430 on the symbol 528 may be vulnerable to interference fromthe NACK transmitted by second UE 420 on the different frequency ifthere is sufficient power leakage.

At symbol 14 of slot 3, second UE 420 may switch from the transmittingmode back to the receiving mode. During the same symbol, third UE 430may terminate transmitting by using a gap symbol 530.

During slot 4, UEs may contend for access to the transmission resourcesby transmitting a LBT sequence 520 during symbol 1 and during symbol 3.First UE 410 may utilize the transmission resources for a one slottransmission.

Again, first UE 410 reserve symbol 13 of its first slot of the one slottransmission for use by any UEs for transmitting a NACK if any UEs wereunable to correctly decode the data packet received in the previoustransmission. As depicted in timeline 512, if second UE 420 could notcorrectly decode the data packet transmitted from third UE 430 duringthe previous transmission, second UE 420 may transmit a NACK during theNACK feedback symbol 526 slot 4. However, second UE 420 may transmit theNACK to third UE 430 on a different frequency than that used by UE 410to receive its NACK.

During symbol 13 of the transmission slot of first UE 410 in slot 4,first UE 410 refrains from transmitting. The NACK transmitted fromsecond UE 420 may be received by third UE 430 to indicate that the datapacket transmitted during the previous one slot transmission slot wasnot correctly decoded by second UE 420. Third UE 430 may contend fortransmission resources following the one slot transmission by first UE410 to retransmit the data packet. At symbol 14 of the transmission offirst UE 410, second UE 420 may switch from the transmitting mode backto the receiving mode. During the same symbol, first UE 410 mayterminate transmitting by using a gap symbol 530.

In FIG. 5 , symbol 13 of the first transmission slot after the end of aprevious transmission may be reserved for the NACK feedback symbol 526.In one aspect, the symbol number and the number of slots between the endof the previous transmission and the NACK transmission may beconfigurable. For example, if additional decoding time is needed byreceiving UEs to decode a data packet received in the previoustransmission, the NACK feedback symbol 526 may be moved to the second ora subsequent slot after the end of the previous transmission. In oneaspect, if a receiving UE has a NACK to transmit, the receiving UE maynot contend for the transmission resources until the receiving UEtransmits the NACK. For example, if second UE 420 has data packets totransmit and wishes to acquire the transmission resources, second UE 420may transmit the NACK to respond to unsuccessful decoding of a datapacket received in a previous transmission before second UE 420 utilizesthe transmission resources to transmit its own data packets.

FIG. 6 is a diagram illustrating transmissions of NACKs forHARQ-feedback in the second symbol of a second slot after the end of atransmission (e.g., a first transmit slot following a previoustransmission) in accordance with certain aspects of the disclosure. Inthe five slot transmission resources depicted in timeline 610, a UE maybe in a transmitting mode for two slots followed by two slots duringwhich the UE is in the receive mode, which is then followed by one slotduring which the UE is again in the transmitting mode. For example, theUE may be first UE 410 of FIGS. 4A-4C. As in FIG. 5 , UEs may contendfor access to transmission resources by transmitting LBT sequences 520during symbol 1 and symbol 3 of the slot. As in FIG. 5 , the first UE410 utilizes the transmission resources and may transmit controlinformation, reference signals, and a data packet in an aggregation oftwo transmitting slots that includes the first and the second slot.

However, unlike FIG. 5 , symbol 2 of the second slot following the endof a previous transmission may be reserved as the NACK feedback symbol526 for use by any UEs for transmitting a NACK in response to the UEsnot being able to correctly decode a data packet received in a previoustransmission. For example, if second UE 420 could not correctly decode adata packet received from first UE 410 or from other UEs, during anaggregation of one or more transmitting slots that precedes the currenttwo slot aggregation in slots 1 and 2, second UE 420 may transmit a NACKduring the NACK feedback symbol 526 in symbol 2 of the second slot ofthe current two slot aggregation. This may be illustrated by timeline612 for second UE 420.

In timeline 612, the second UE 420 may receive the transmission fromfirst UE 410 during symbols 2, and 4-14 of the first slot of the twoslot aggregation used by first UE 410 for transmitting. At symbol 1 ofthe second slot, one symbol before the NACK feedback symbol 526, secondUE 420 may switch from the receiving mode to the transmitting mode usinga gap symbol 530. Because symbol 1 may be used by UEs to transmit LBTsequences for access contention of the transmission resources, first UE410 might not transmit its data packet using symbol 1. As such, first UE410 does not puncture its transmission of the data packet during symbol1.

During the NACK feedback symbol 526, first UE 410 refrains fromtransmitting. The NACK transmitted from second UE 420 may be received byfirst UE 410 to indicate that data packet transmitted in a transmissionprior to the current two slot aggregation was not correctly decoded bysecond UE 420 if the prior transmission was from first UE 410. First UE410 may contend for transmission resources following the current twoslot aggregation to retransmit the data packet that was not successfullydecoded by second UE 420 in a later transmission. In one aspect, if thetransmission prior to the current two slot aggregation was from anotherUE, and if first UE 410 did not correctly decode the data packettransmitted in the prior transmission, first UE 410 may transmit a NACKusing the NACK feedback symbol 526 to request retransmission from the UEtransmitting in the prior transmission.

At symbol 3 of the second slot of the two slot aggregation, one symbolafter the NACK feedback symbol 526, second UE 420 may switch from thetransmitting mode back to the receiving mode using another gap symbol530. Because symbol 3 may also be used by UEs to transmit LBT sequencesfor access contention of the transmission resources, first UE 410 mightnot transmit its data packet using symbol 3. As such, first UE 410 alsoneed not puncture its transmission of the data packet during symbol 3.First UE may continue to transmit the data packet during symbols 4-13 ofthe second slot of the two slot aggregation. During symbol 14 of thesecond transmitting slot of the two slot aggregation, first UE 410 maytransition from the transmitting mode to a receiving mode by using a gapsymbol 530. In one aspect, if LBT sequences are not transmitted insymbol 1 or symbol 3 of the slot, symbol 1 or symbol 3 may be filledafter all other symbols in the aggregation of transmitting slots arefilled with code rate matched data from a buffer. In one aspect,residual data following code rate matching may be transmitted in symbols1 and 3 after the remaining symbols (e.g., symbols 4-14) in the slot arefilled if LBT sequences are not transmitted in symbols 1 and 3 of theslot.

At slot 3, after first UE 410 has completed transmitting, UEs maycontend for access to the transmission resources by transmitting a LBTsequence 520 during symbol 1 and symbol 3. For example, as depicted intimeline 614, third UE 430 may transmit a LBT sequence 520 during thethird symbol for LBT counter 1 to contend for access to the transmissionresources. If third UE 430 utilizes the transmission resources, third UE430 may use one or more slots for transmitting. For example, third UE430 may transmit control information, reference signals, and a datapacket using slot 3 in a one slot transmission. Because the NACKfeedback symbol 526 is reserved for symbol 2 of a second transmittingslot, and because third UE 430 is transmitting for only one slot, thirdUE 430 does not reserve any symbol in the one transmitting slot for theNACK feedback symbol 526. As such, third UE 430 may transmit on symbols4-13 of the one transmitting slot. Third UE 430 may transition from thetransmitting mode to a receiving mode by using a gap symbol 530 atsymbol 14.

If second UE 420 could not correctly decode the data packet transmittedfrom first UE 410 during the two slot aggregation used by first UE 410for transmitting, second UE 420 may transmit a NACK during the NACKfeedback symbol 526 of the second slot following the end of thetransmission from first UE 410 (e.g., slot 4), as depicted in timeline614. The NACK transmitted from second UE 420 may be received by first UE410 to indicate that the data packet transmitted during the two slotaggregation was not correctly decoded by second UE 420. First UE 410 maycontend for transmission resources to retransmit the data packet.

During the fifth slot of the transmission resources, UEs may contend foraccess to the transmission resources by transmitting a LBT sequence 520during symbol 1 and symbol 3. First UE 410 may utilize the transmissionresources for a one slot transmission.

If second UE 420 could not correctly decode the data packet transmittedfrom third UE 430 during the one slot used by third UE 430 fortransmitting, second UE 420 may transmit a NACK during the NACK feedbacksymbol 526 of the second slot following the end of the transmission fromthird UE 430, as depicted in timeline 612. This slot is shown as thefifth slot of the transmission resources and is utilized by first UE 410for the one slot transmission. The NACK transmitted from second UE 420may be received by third UE 430 to indicate that the data packettransmitted during the one slot transmission was not correctly decodedby second UE 420. Third UE 430 may contend for transmission resources toretransmit the data packet following the current one slot transmissionby first UE 410.

In FIG. 6 , symbol 2 of the second transmission slot after the end of aprevious transmission is reserved for the NACK feedback symbol 526. Inone aspect, the symbol number and the number of slots between the end ofthe previous transmission and the NACK transmission may be configurable.For example, if additional decoding time is needed by receiving UEs todecode a data packet received in the previous transmission, the NACKfeedback symbol 526 may be moved to the third or a subsequent slot afterthe end of the previous transmission. In one aspect, if a receiving UEhas a NACK to transmit, the receiving UE may not contend for thetransmission resources until the receiving UE transmits the NACK. Forexample, if second UE 420 has data packets to transmit and wishes toacquire the transmission resources, second UE420 may transmit the NACKto respond to unsuccessful decoding of a data packet received in aprevious transmission before second UE 420 acquires the transmissionresources to transmit its own data packets.

FIG. 7 is a diagram illustrating transmissions of NACKs forHARQ-feedback and the use of a turnaround time in accordance withcertain aspects of the disclosure. In FIG. 7 , the turnaround time for areceiving UE to switch from a receiving mode to a transmitting mode totransmit a NACK, the transmitting of the NACK, and the turnaround timefor the receiving UE to switch from the transmitting mode back to thereceiving mode are all combined into one symbol.

In the three slot transmission resources depicted in timeline 710, a UEmay be in a transmitting mode for two slots followed by one slot duringwhich the UE is in another transmitting mode. A gap symbol 730 may beprovided between the two slot aggregation and the following transmissionslot. For example, the UE may be first UE 410 of FIGS. 4A-4C. First UE410 may contend for access to transmission resources by transmitting LBTsequences 720 during symbols 1, 2, and 3 of the slot. First UE 410 mayutilize the transmission resources and may transmit control informationin a control symbol 732 in symbol 4, and may transmit reference signalsand a data packet in symbols 5-13 of a first slot and in symbols 1-13 ofa second slot of an aggregation of two transmitting slots.

Symbols 14 of the first slot following the end of a previoustransmission may be reserved as the NACK feedback symbol 726 for use byany UEs for transmitting a NACK in response to the UEs not being able tocorrectly decode a data packet received in a previous transmission. Forexample, if second UE 420 could not correctly decode a data packetreceived from another UE during an aggregation of one or moretransmitting slots that precedes the current two slot aggregation,second UE 420 may transmit a NACK during the NACK feedback symbol 726 insymbol 14 of the first slot of the current two slot aggregation. Thismay be illustrated by timeline 712 for second UE 420. However, unlike inFIG. 5 and FIG. 6 , second UE 420 may use a first part of symbol 14 toswitch from the receiving mode to the transmitting mode, transmit theNACK during a second part of symbol 14, and use a third part of symbol14 to switch from the transmitting mode back to the receiving mode. Forexample, second UE 420 may switch from the receiving mode to thetransmitting mode during the first quarter of the symbol time of symbol14. UE 420 may transmit the NACK signal during the second and thirdquarters of the symbols time of symbol 14. UE 420 may then switch fromthe transmitting mode back to the receiving mode during the last quarterof the symbol time of symbol 14.

By transmitting the NACK in half of the symbol time of symbol 14, thesubcarrier spacing of symbols is doubled and the number of subcarriersavailable for NACK transmission is consequently reduced by a half. As aresult, instead of having 12 subcarriers in a resource block of a symbolavailable for use for transmission, the number of available subcarriersis reduced to 6. However, by transmitting in only a portion of thesymbol time of the NACK feedback symbol, second UE 420 may turnaroundfrom receiving to transmitting, transmit the NACK, and turnaround fromtransmitting back to receiving all within one symbol when transmittingthe NACK. In one aspect, up to two bits for a NACK may be transmitted intwo subcarriers.

FIG. 8 is a diagram illustrating transmissions of NACKs forHARQ-feedback in dedicated NACK symbols after every N slots inaccordance with certain aspects of the disclosure. In FIG. 8 , NACKs fordata packets or transport blocks in multiple slots may be multiplexedand transmitted in the same NACK feedback symbol. The NACK feedbacksymbol may be a dedicated system wide symbol used by any receiving UEsto transmit NACKs for data packets that were unsuccessfully decode inthe previous N slots. For example, a set of symbols may be dedicated forswitching modes and transmitting NACKs. FIG. 8 illustrates a set ofthree symbols. This is merely an example, and the set of symbols mayinclude a different number of symbols. The three symbols may include afirst turnaround symbol 830 to allow a receiving UE to switch from thereceiving mode to the transmitting mode, a NACK feedback symbol 826 fortransmitting the NACK signals, and a second turnaround symbol 830 toswitch from the transmitting mode back to the receiving mode. In oneaspect, N is configurable.

FIG. 9A is a first diagram illustrating transmissions of NACKs forHARQ-feedback in dedicated NACK symbols after every N slots inaccordance with certain aspects of the disclosure. In the five slottransmission resources depicted in timeline 910, a UE may be in atransmitting mode for two slots followed by two slots during which theUE is in the receive mode, which is then followed by one slot duringwhich the UE is again in the transmitting mode. For example, the UE maybe first UE 410 of FIGS. 4A-4C. UEs may contend for access totransmission resources by transmitting LBT sequences 920 during thefirst three symbols of the slot. Therefore, some symbols 922 of aparticular UE may be vulnerable to LBT sequences transmitted by othercontending UEs. First UE 410 may utilize the transmission resources andmay transmit control information, reference signals, and a data packetin an aggregation of two transmitting slots that includes the first andthe second slot.

Because dedicated NACK symbols are used to transmit NACKs, first UE 410may transmit from symbol 4 of the first slot until symbol 13 of thesecond slot of the two slot aggregation. During slot 3, after first UE410 has completed transmitting, UEs may contend for access to thetransmission resources by transmitting a LBT sequence 920 during thefirst three symbols of the slot. For example, as depicted in timeline914, third UE 430 may transmit a LBT sequence 920 during the first threesymbols to contend for access to the transmission resources. Third UE430 may use one or more slots of the transmission resources fortransmitting. For example, third UE 430 may transmit controlinformation, reference signals, and a data packet using the third slotof the transmission resources in a one slot transmission. Again, becausededicated NACK symbols are used to transmit NACKs, third UE 430 maytransmit from symbol 4 until symbol 13 of the third slot.

After the three slots of transmission, three symbols are dedicated forNACK transmission. For example, a first turnaround symbol 930 may beused to allow a receiving UE to switch from the receiving mode to thetransmitting mode, a NACK feedback symbol 926 may be used fortransmitting the NACK signals, and a second turnaround symbol 930 may beused to switch from the transmitting mode back to the receiving mode. Ifsecond UE 420 could not correctly decode the data packet transmittedfrom first UE 410 during the two slot aggregation used by first UE 410for transmitting, or if second UE 420 could not correctly decode thedata packet transmitted from third UE 430 during its one slottransmission, second UE 420 may transmit NACK signals using the threededicated symbols for NACK transmission as depicted in timeline 912. InFIG. 9A, the three dedicated symbols are shown as part of a slot (e.g.,in symbols 12-14 of a slot). In one aspect, the three dedicated symbolsmay be standalone symbols that are not part of any slot.

In FIG. 9A, the dedicated NACK symbols in slot 4 are used by UEs to sendNACKs in response to data packets received by the UEs in slots 1-3.Because the dedicated NACK symbols are part of a regular slot structure,data packets may be transmitted during the remaining symbols (e.g.,symbols 1-11) of the slot containing the dedicated NACK symbols (e.g.,slot 4). NACKs for data packets transmitted during these symbols may betransmitted during the next dedicated NACK symbols. As such, thededicated NACK symbols in slot 4 may also be used to send NACKs inresponse to data packets received in the slot that contains the previousdedicated NACK symbols, e.g., a slot preceding slot 1. In one aspect, ifthe dedicated NACK symbols occur every N slots, the dedicated NACKsymbols may be used to transmit NACKs for data packets received duringthe window of slots from slots 1 to slot N-1, the following dedicatedNACK symbols may be used to transmit NACK from slot N to slot 2N-1, andso forth. For example, in FIG. 9A, the dedicated NACK symbols in slot 4may be used to transmit NACKs for data packets received during thewindow of slots 0, 1,2, 3 if the number of slots between dedicated NACKsymbols, N, is 4. In one aspect, for dedicated symbols at slot M, thededicated NACK symbols may be used to transmit NACKS for data packetsreceived during the window of slots (M-N-1) ... (M-2) if data packetdecoding latency of the receiving device is large. M, N, and the offsetby which the window of slots containing the data packets are offset fromM may be configurable.

FIG. 9B is a first diagram illustrating example transmissions of NACKsfor HARQ-feedback in dedicated NACK symbols, e.g., after every 3 slotsin accordance with certain aspects of the disclosure. In FIG. 9B, thethree dedicated NACK symbols are standalone symbols that are not part ofa slot. For example, the two turnaround symbols 930 and the NACKfeedback symbol 926 are not part of a regular slot. The three dedicatedNACK symbols may be used by UEs to respond to data packets received bythe UEs in the first three slots. The number of slots between thededicated NACK symbols, N, and the offset by which the window of slotscontaining the data packets is offset from the dedicated NACK symbolsmay be configurable.

FIG. 10 illustrates aspects of feedback channels containing NACKs formulticast and unicast transmissions in accordance with certain aspectsof the disclosure. In one aspect, reference signals for the NACK signalsmay be transmitted in a comb-4 pattern, or in one of every foursubcarriers of a NACK feedback symbol, as shown in table 1010. Referencesignals may be used by the UE receiving the NACK signals for estimatingthe channels. The NACKS signal may be carried on the other subcarriers.In one aspect, for multicast transmission, only one bit representing theNACK may be required. The NACK may use repetition coding using the sameLBT sequence that was used to represent the of the transmissionresources. In some examples, the NACK may include one or more additionalfeedback bits transmitted in the NACK feedback symbol. For unicasttransmissions, additional feedback signals may be transmitted. In oneaspect, assuming a granularity of 10 RB, the feedback channel maycontain 18 bits of information. The modulation coding scheme used forthe feedback channel may be QPSK ½ with a coding rate of ⅒^(th). In oneaspect polar coding may be used, similar to that used for the controlinformation. Table 1020 shows that in unicast transmissions, up to 12bits may be transmitted. The number of feedback bits depends on the typeof feedback. For example, only three bits may be required if feedback ofonly RI and NACK is desired. In another example, 8 bits may be requiredif feedback of RI, CQI, and NACK is desired.

FIG. 11 is a call flow diagram 1100 illustrating an implementation ofdata packet transmissions from a transmitting UE and NACKs forHARQ-feedback from a receiving UE in accordance with certain aspects ofthe disclosure. The communication between UEs may be based on any ofV2V, V2X, and/or other D2D communication. While these aspects areillustrated using the example of a first UE 410 and a second UE 420, theaspects are equally applicable to other types of UEs and othertransmitting and receiving devices engaged in V2V, V2X, and/or other D2Dcommunication. The UE transmitting the data packet may be first UE 410of FIGS. 4A-4C. The UE transmitting the NACK may be the second UE 420 ofFIG. 4 .

At 1102, first UE 410 has a data packet to transmit and may contend foraccess to transmission resources. For example, first UE 410 may transmita LBT sequence during the first symbol of a slot. Other UEs may contendfor the transmission resources by transmitting their LBT sequences.Then, first UE 410 may utilize the transmission resources, e.g., a slotor an aggregation of slots, for transmitting control and a first datapacket 1104. At 1108, first UE 410 may complete transmitting the firstdata packet 1104.

At 1106, second UE 420 may receive the first data packet 1104transmitted by first UE 410 during the one or more slots. Second UE 420may determine if the first data packet 1104 is correctly received byperforming a CRC on the received data. If the CRS fails, second UE 420may determine the first data packet 1104 to have been receivedincorrectly. Second UE 420 may wait until the end of the one or moreslots. In one aspect, second UE 420 may require additional time toperform the CRC and second UE 420 may not be able to determine that thefirst data packet 1104 was received incorrectly until some delay afterthe end of the one or more slots during which the first data packet 1104was transmitted.

After first UE 410 completes transmitting the first data packet duringthe one or more slots, first UE 410 may enter into a reception mode in1110 if it does not have any additional data packets to transmit. Duringthe reception mode 1110, first UE 410 may listen to transmissions fromother UEs, including listening for any NACK transmitted by second UE 420or any other UEs. Alternatively, first UE 410 may have additional datapackets to transmit and may again contend for transmission resources bytransmitting LBT sequences during the first slot of a slot in 1112.After performing the LBT sequence, UE 410 may use one slot or anaggregation of slots for transmitting control and a second data packet1114.

At 1116, first UE 410 may reserve a feedback symbol of a configured slotfor use by UEs for transmitting NACK feedback when unable to correctlydecode the first data packet 1104 received in the previous transmissionfrom first UE 410. First UE 410 may refrain from transmitting during thefeedback symbol of the configured slot. In one aspect, the configuredslot may be configured to be N slots after the end of the previoustransmission.

Second UE 420 may receive the second data packet 1114 and may determineif the second data packet 1114 is received correctly. If second UE 420has a NACK signal to transmit because the first data packet 1104 was notreceived correctly, second UE 420 may switch from the receiving mode tothe transmitting mode prior to the feedback symbol of the configuredslot. In one aspect, second UE 420 may switch from the receiving mode tothe transmitting mode in the symbol prior to the feedback symbol of theconfigured slot at 1118. In one aspect, second UE 420 may switch fromthe receiving mode to the transmitting mode in the same symbol as thefeedback symbol of the configured slot but before the start oftransmission of the NACK. Second UE may transmit the NACK for the datapacket in the feedback symbol of the configured slot at 1120.

At 1124, second UE 420 may switch from the transmitting mode back to thereceiving mode after transmitting the NACK. In one aspect, second UE 420may switch from the transmitting mode back to the receive mode in thesymbol after the feedback symbol of the configured slot at 1124. In oneaspect, second UE 420 may puncture the portion of the second data packet1114 received from first UE 410 during the symbol after the feedbacksymbol of the configured slot. In one aspect, second UE 420 may switchfrom the transmitting mode back to the receiving mode in the same symbolas the feedback symbol of the configured slot but after the end oftransmission of the NACK.

First UE 410 may listen to any NACK transmitted by second UE 420 or anyother UEs during the feedback symbol of the configured slot if first UE410 also transmitted in the previous transmission. For example, the NACKtransmitted by second UE 420 may indicate to first UE 410 to retransmitthe first data packet 1104 that was transmitted in the previoustransmission because second UE 420 was not able to receive the firstdata packet 1104 correctly. If first UE 410 did not transmit in theprevious transmission, first UE 410 may ignore any NACKs received duringthe feedback symbol of the configured slot.

At 1122, after the feedback symbol of the configured slot, first UE 410may resume transmitting the second data packet 1114 during the one ormore transmitting slots. In one aspect, to accommodate NACK transmittingUEs without compromising the data rate of other UEs that do not transmitNACKs in the feedback symbol of a configured slot, first UE 410 may fillthe symbols prior and after the feedback symbols in every slot after allother symbols in the aggregation of transmitting slots are filled withcode rate matched data from a buffer.

FIG. 12 is a flowchart of a method 1200 of wireless communication thatinvolves receiving data packets from a transmitting UE and transmittingfeedback that may be implemented by a receiving UE in accordance withcertain aspects of the disclosure. The method may be performed by adevice engaged in V2V/V2X/D2D communication, e.g., UE or a component ofa UE 104, 410, 420, 430; the device 350; the apparatus 1300, 1300′; theprocessing system 1414, which may include memory 1406 and one or more ofRX processor 356, 370, TX processor 316, 368, or controller/processor359, 375. Additional devices engaged in V2V/V2X communication may alsoperform the method, e.g., an RSU, base station, etc. The method mayprovide more reliable communication, by enabling communication devicesengaged in TDD communication to more effectively provide NACK feedback.In V2V/V2X/D2D communication, receiving devices may transmit only NACKfeedback. In other words, transmitting devices may assume that thetransmitted data packets are successfully received by receiving devicesunless NACK feedback is received.

The method allows a receiving device that does not receive the datapackets correctly from a transmitting device to transmit a NACK to thetransmitting device during a portion of a receiving slot in which thereceiving device may receive additional data packets from othertransmissions. The receiving device may switch from a receiving mode toa transmitting mode, transmit the NACK, and switch from the transmittingmode back to the receiving mode to continue receiving data packets. Themethod provides a way for the receiving device to transmit the NACKwithout compromising the detection performance of other transmissions.

At 1202, a first device may receive from a second device a first datapacket in one or more receiving slots. The reception may be performed,e.g., by the reception component 1312 of the apparatus 1300. The slotsmay be part of a TDD frame that includes a plurality of slots, such asin the example frame structures illustrated in any of FIGS. 5-9 . Aplurality of devices may contend for use of the plurality of slots fortransmission, e.g., using a LBT mechanism. Each slot may include aplurality of symbols.

At 1204, the first device may determine whether the first data packet isreceived incorrectly. The determination may be performed, e.g., by theerror determination component 1302 of the apparatus 1300. In someaspects, the first device may perform a CRC check on the first datapacket. If the CRC fails, the first device may determine that the firstdata packet is received incorrectly and may transmit a NACK to solicitretransmission of the first data packet.

At 1206, the first device may wait until the end of the one or morereceiving slots, such as a receiving device waiting until the end of the2 slot aggregation illustrated in FIG. 5 . The waiting may be performedby the receiving slot component 1304 of the apparatus 1300. In oneaspect, first device may require additional time to perform the CRCcheck, and the first device may not be able to determine that the firstdata packet was received incorrectly until some delay after the end ofthe one or more receiving slots. Thus, the first device may wait untilthe end of more than one receiving slot to send the feedback.

At 1208, the first device may transmit to the second device a NACK in afeedback symbol of a slot after the end of the one or more receivingslots in response to determining that the first packet is receivedincorrectly. The slot may comprise a configured slot. The transmissionmay be performed, e.g., by the NACK feedback control component 1308and/or the transmission component 1310 of the apparatus 1300. Thefeedback symbol of the slot may be reserved for use any UEs fortransmitting a NACK in response to the UEs unable to correctly decodethe first data packet from the second device received during the one ormore receiving slots. In one aspect, the slot may be configured to be Nslots after the end of the one or more receiving slots.

At 1210, the first device may switch from the receiving mode to thetransmitting mode during a first turnaround symbol in the slot in orderto transmit the first NACK in the NACK feedback symbol. The firstturnaround symbol may come one symbol before the feedback symbol. Theswitch may be performed, e.g., by the NACK feedback control component1308 of the apparatus 1300. For example, the first device may switchfrom receiving a second packet in the slot from a third device duringthe receiving mode. In one aspect, first device may switch from thereceiving mode to the transmitting mode in the same symbol as thefeedback symbol of the slot but before the start of transmission of theNACK. Thus, in this aspect, the first device may transmit the first NACKto the second device in a transmitting portion of the NACK feedbacksymbol of the slot. The NACK feedback symbol may include a largersub-carrier spacing than a sub-carrier spacing of other symbols in theone or more receiving slots, and the transmitting portion of the NACKfeedback symbol may be less than a symbol length of the NACK feedbacksymbol. In some aspects, the slot may comprise a first slot that followsthe one or more receiving slots, and the NACK feedback symbol mayinclude a symbol thirteen of the slot. The first turnaround symbol mayinclude symbol twelve of the slot, and the second turnaround symbol mayinclude symbol fourteen of the slot. FIG. 5 illustrates an example ofinclude a NACK feedback symbol at symbol thirteen of the slot. The slotmay include a second slot that is separated from the one or morereceiving slots by at least one slot, and the NACK feedback symbol mayinclude a second symbol of the slot. The first turnaround symbol mayinclude a first symbol of the slot, and the second turnaround symbol mayinclude a third symbol of the slot. FIG. 6 illustrates an example inwhich the NACK feedback symbol includes a second symbol of the slot. Theslot may be at a configurable number of slots after the one or morereceiving slots.

At 1212, the first device may switch from the transmitting mode back tothe receiving mode during a second turnaround symbol in the slot. Thesecond turnaround symbol may come one symbol after the NACK feedbacksymbol. The switch may be performed, e.g., by the NACK feedback controlcomponent 1308 of the apparatus 1300. In one aspect, first device mayswitch from the transmitting mode back to the receiving mode in the samesymbol as the feedback symbol of the slot but after the end oftransmission of the NACK. The first device may further switch to thetransmitting mode to transmit a third packet in a subsequent slotfollowing the slot after transmitting the first NACK in the NACKfeedback symbol in the slot.

The first device may use a set of dedicated symbols that are reservedfor NACK, e.g., in a system wide manner, such as described in connectionwith FIG. 8 . Occurrences of the set of dedicated symbols for NACK mayoccur every N slots. Thus at 1214, the first device may transmit theNACK using a NACK feedback symbol that comprises a symbol every N slotsof the TDD frame. In one aspect, dedicated NACK symbols after every Nslots may be used for transmitting NACKs for data packets that wereunsuccessfully decode in the previous N slots. The NACKs for the datapacket transmitted in the N slots may be multiplexed and transmitted inthe dedicated NACK symbol. N may be a configurable parameter. Forexample, a set of symbols, such as three symbols, may be dedicated forNACK, as described in connection with FIG. 8 . The three symbols mayinclude a first turnaround symbol to allow a receiving UE to switch fromthe receiving mode to the transmitting mode, a NACK feedback symbol fortransmitting the NACK signals, and a second turnaround symbol to switchfrom the transmitting mode back to the receiving mode.

At 1216, the first device may transmit the NACKS a number of slots afterthe end of the one or more receiving slots. The transmission may beperformed, e.g., by the transmission component 1310 of the apparatus1300. The slot may be configurable to allow sufficient time for thefirst device to determine if any data packet is received in error duringthe one or more receiving slots. In one aspect, the slot may be thefirst slot after the end of the one or more receiving slots and thefeedback symbol may be symbol 13. In one aspect, the slot may be thesecond slot after the end of the one or more receiving slots and thefeedback symbol may be symbol 2.

The first device may receive one or more additional data packets from athird device in the one or more receiving slots. The first device maysimilarly determine whether the one or more additional data packets arereceived correctly. The first device may transmit to the third device anadditional NACK with the first NACK in the NACK feedback symbol in theslot in response to determining that the one or more additional datapackets are received incorrectly. A number of the one or more receivingslots may be configurable for receiving the first data packet and theone or more additional data packets.

The NACK that is transmitted at 1208 may include one or more additionalfeedback bits transmitted in the NACK feedback symbol. The one or moreadditional feedback bits may be transmitted by the first device in aunicast transmission. The one or more additional feedback bits mayinclude a reference signal that is transmitted by the first device onone of every N subcarriers of the NACK feedback symbol.

FIG. 18 is a flowchart of a method 1800 of wireless communication thatinvolves receiving data packets from a transmitting UE and transmittingfeedback that may be implemented by a receiving UE in accordance withcertain aspects of the disclosure The method may be performed by adevice engaged in V2V/V2X/D2D communication, e.g., UE or a component ofa UE 104, 410, 420, 430; the device 350; the apparatus 1300, 1300′; theprocessing system 1414, which may include memory 1406 and one or more ofRX processor 356, 370, TX processor 316, 368, or controller/processor359, 375. Additional devices engaged in V2V/V2X communication may alsoperform the method, e.g., an RSU, base station, etc. In FIG. 18 , thereceiving device may use a dedicated set of at least one symbol totransmit the NACK. The dedicated set of symbols may comprise a systemwide dedicated symbol, e.g., as described in connection with FIG. 8 .

At 1802, the receiving device receives from a second device a first datapacket in one or more receiving slots of a TDD frame that includes aplurality of slots, wherein a slot includes a plurality of symbols,e.g., such as described in connection with 1202 in FIG. 12 . Thereception may be performed, e.g., by the reception component 1312 of theapparatus 1300.

At 1804, the receiving device determines whether the first data packetis received incorrectly. For example, the determination may includeaspects described in connection with 1204 in FIG. 12 . The determinationmay be performed, e.g., by the error determination component 1302 of theapparatus 1300.

At 1806, the receiving device may wait until a set of dedicated symbolsto transmit a first NACK. The wait may be performed, e.g., by the NACKfeedback control component 1308 of the apparatus 1300. The set ofdedicated symbols may be reserved by a communication system, e.g., in asystem wide manner, for feedback. The set of dedicated symbols maycomprise occurrences spaced by a number of N slots, e.g., as describedin connection with FIG. 8 . Each occurrence of the set of dedicatedsymbols comprises at least three symbols, e.g., a NACK/feedback symbol,and at least one surrounding symbol before and after the NACK/feedbacksymbol. FIG. 9A illustrates an example in which the set of dedicatedsymbols may be symbols within one of the N slots. For a spacing of Nslots, the dedicated resources may be used for NACK for the slots fromslot 1 to slot N-1. FIG. 9B illustrates an example in which the set ofdedicated symbols are provided separate from a slot. The set ofdedicated symbols may include symbols within one of the plurality ofslots. The set of dedicated symbols may include standalone symbolsoutside of the plurality of slots. The one or more receiving slotscontaining the first data packet for which the NACK is transmitted maybe offset from the set of dedicated symbols by one or more offset slots.The one or more offset slots may be configurable.

At 1808, the receiving device may transmit to the second device thefirst NACK in a NACK feedback symbol in the set of dedicated symbolsafter the end of the one or more receiving slots in response todetermining that the first data packet is received incorrectly. Thetransmission may be performed, e.g., by the transmission component 1310of the apparatus 1300.

FIG. 13 is a conceptual data flow diagram illustrating the data flowbetween different modules/means/components in an example apparatus 1300of a receiving device in accordance with certain aspects of thedisclosure. The apparatus 1300 may comprise a UE or a component of a UEor another receiving device engaged in V2V, V2X, or other D2Dcommunication. The apparatus 1300 may include a transmission component1310, an error determination component 1302, a receiving slot component1304, a NACK feedback slot component 1306, a NACK feedback controlcomponent 1308, and a reception component 1312.

The error determination component 1302 may be configured to determine ifa first data packet is received incorrectly, e.g., as described inconnection with 1204 in FIG. 12 or 1804 in FIG. 18 . The receiving slotcomponent 1304 may be configured to determine if the end of the one ormore receiving slots during which the first data packet is received hasbeen reached, e.g., as described in connection with 1206 in FIG. 12 . Inone aspect, the receiving slot component 1304 may be configured todetermine that the error determination component 1302 has not completeddetermining that the first data packet is receive incorrectly until somedelay after the end of the one or more receiving slots. The NACKfeedback slot component 1306 may be configured to determine or selectthe slot for transmitting the NACKS to be a number of slots after theend of the one or more receiving slots. The determined slot may beselected to allow sufficient time for the first device to determine ifany data packet is received in error during the one or more receivingslots. In one aspect, the determined slot may be the first slot afterthe end of the one or more receiving slots and the feedback symbol maybe symbol 13. In one aspect, the determined slot may be the second slotafter the end of the one or more receiving slots and the feedback symbolmay be symbol 2. In one aspect, the NACK feedback slot component 1306may be configured to determine the slot for transmitting the NACK to beevery N slots. In one aspect, dedicated NACK symbols after every N slotsmay be used for transmitting NACKs for data packets that wereunsuccessfully decode in the previous N slots. The NACKs for the datapacket transmitted in the N slots may be multiplexed and transmitted inthe dedicated NACK symbol. For example, three symbols may be dedicatedfor NACK. The three symbols may include a first turnaround symbol toallow a receiving UE to switch from the receiving mode to thetransmitting mode, a NACK feedback symbol for transmitting the NACKsignals, and a second turnaround symbol to switch from the transmittingmode back to the receiving mode. In one aspect, N is configurable.

The NACK feedback control component 1308 may be configured to transmit aNACK in a feedback symbol of the configured slot. In one aspect, theNACK feedback control component 1308 may be configured to switch theapparatus 1300 from the receiving mode to the transmitting mode in thesymbol prior to the feedback symbol of the configured slot. In oneaspect, the apparatus 1300 may switch from the receiving mode to thetransmitting mode in the same symbol as the feedback symbol of theconfigured slot but before the start of transmission of the NACK. In oneaspect, the NACK feedback control component 1308 may be configured toswitch the apparatus 1300 from the transmitting mode back to the receivemode in the symbol after the feedback symbol of the configured slot. Inone aspect, the apparatus 1300 may switch from the transmitting modeback to the receiving mode in the same symbol as the feedback symbol ofthe configured slot but after the end of transmission of the NACK.

The transmission component 1310 may be configured to transmit the NACKin the feedback symbol of the configured slot to a second device 1350.The reception component 1312 may be configured to receive the transportblock of the data packet from the second device 1350.

The apparatus may include additional components that perform each of theblocks of the algorithm in the aforementioned flowcharts of FIGS. 11,12, and/or 18 . As such, each block in the aforementioned flowcharts ofFIGS. 11, 12, and/or 18 may be performed by a component and theapparatus may include one or more of those components. The componentsmay be one or more hardware components specifically configured to carryout the stated processes/algorithm, implemented by a processorconfigured to perform the stated processes/algorithm, stored within acomputer-readable medium for implementation by a processor, or somecombination thereof.

FIG. 14 is a diagram illustrating an example of a hardwareimplementation 1400 for an apparatus 1300′ of a receiving UE employing aprocessing system 1414 in accordance with certain aspects of thedisclosure. The processing system 1414 may be implemented with a busarchitecture, represented generally by the bus 1408. The bus 1408 mayinclude any number of interconnecting buses and bridges depending on thespecific application of the processing system 1414 and the overalldesign constraints. The bus 1408 links together various circuitsincluding one or more processors and/or hardware components, representedby the processor 1404, the transceiver 1410, components 1304, 1306,1308, 1310, 1312, and the computer-readable medium / memory 1406. Thebus 1408 may also link various other circuits such as timing sources,peripherals, voltage regulators, and power management circuits, whichare well known in the art, and therefore, will not be described anyfurther.

The processing system 1414 may be coupled to a transceiver 1410. Thetransceiver 1410 is coupled to one or more antennas 1420. Thetransceiver 1410 provides a means for communicating with various otherapparatus over a transmission medium. The transceiver 1410 receives asignal from the one or more antennas 1120, extracts information such asthe received data packets, and provides the extracted information to theprocessing system 1414, specifically error determination component 1302.In addition, the transceiver 1410 receives information from theprocessing system 1414, specifically the NACK in the feedback symbol ofthe configured slot, and based on the received information, generates asignal to be applied to the one or more antennas 1420. The processingsystem 1414 includes a processor 1404 coupled to a computer-readablemedium / memory 1406. The processor 1404 is responsible for generalprocessing, including the execution of software stored on thecomputer-readable medium / memory 1406. The software, when executed bythe processor 1404, causes the processing system 1414 to perform thevarious functions described supra for any particular apparatus. Thecomputer-readable medium / memory 1406 may also be used for storing datathat is manipulated by the processor 1404 when executing software. Theprocessing system further includes at least one of the components 1302,1304, 1306, 1308, 1310, 1312. The components may be software componentsrunning in the processor 1404 configured to perform the statedprocesses/algorithm, resident/stored in the computer readable medium /memory 1406 for implementation by the processor 1404, one or morehardware components specifically configured to carry out the statedprocesses/algorithm, one or more hardware components coupled to theprocessor 1404, or some combination thereof. The processing system 1414may be a component of the device 310 or the device 350 and may includethe memory 376, 360 and/or at least one of the TX processor 316, 368,the RX processor 370, 356, and the controller/processor 375, 359.Alternatively, the processing system may comprise an entire UE.

In one configuration, the apparatus 1300′ may include means fordetermining if a first data packet is received incorrectly. The meansfor determining if a first data packet is received incorrectly may beimplemented by the error determination component 1302. The apparatus1300′ may include means for determining the end of the receiving slots.The means for determining the end of the receiving slots may beimplemented by the receiving slot component 1304. The apparatus 1300′may include means for determining the slot for transmitting the NACKS tobe a number of slots after the end of the one or more receiving slots.The means for determining the slot for transmitting the NACKS to be anumber of slots after the end of the one or more receiving slots may beimplemented by the NACK feedback slot component 1306. The apparatus1300′ may include means for transmitting a NACK in a feedback symbol ofthe configured slot. The means for transmitting a NACK in a feedbacksymbol of the configured slot may be implemented by the NACK feedbackcontrol component 1308.

The aforementioned means may be one or more of the aforementionedcomponents of the apparatus 1300 and/or the processing system 1414 ofthe apparatus 1300′ configured to perform the functions recited by theaforementioned means. As described supra, the processing system 1414 mayinclude the TX processor 316, 368, the RX processor 370, 356, and thecontroller/processor 375, 359. As such, in one configuration, theaforementioned means may be the TX processor 316, 368, the RX processor370, 356, and the controller/processor 375, 359 configured to performthe functions recited by the aforementioned means.

FIG. 15 is a flowchart of a method 1500 for transmitting data packets,e.g., multicast data packets, and receiving feedback from at least onereceiving device. The method may be performed by a device engaged inV2V/V2X/D2D communication, e.g., UE or a component of a UE 104, 410,420, 430; the device 350; the apparatus 1600, 1600′; the processingsystem 1714, which may include memory 1406 and one or more of RXprocessor 356, 370, TX processor 316, 368, or controller/processor 359,375. Optional aspects are illustrated with a dashed line. The method mayprovide more reliable communication, by enabling communication devicesengaged in TDD communication to more effectively receiving NACKfeedback.

At 1502, the first device may contend for use of one or more slots of aTDD frame for transmitting, where each slot of the one or more slotsincludes a plurality of symbols. The contention may be performed, e.g.,by the contention component 1602 of the apparatus 1600. For example, thefirst UE may transmit a LBT sequence during the first symbol of a slot.Other UEs may contend for the transmission resources by transmittingtheir LBT sequences. After performing the LBT sequence, the first devicemay use one transmitting slot or an aggregation of transmitting slotsfor transmitting control and a first data packet.

At 1504, the first device may transmit at least a portion the first datapacket during the one or more transmitting slots. The transmission maybe performed, e.g., by the transmission component 1612 and/or the datapacket transmission control component 1608 of the apparatus 1600. Thefirst device may transmit the first data packet as a multicasttransmission to multiple receivers within a receiving distance of thefirst device.

At 1506, the first device may reserve a feedback symbol in a firsttransmitting slot of the one or more slots for reception of a NACK fromone or more devices. Thus, the first device may reserve a feedbacksymbol of a configured slot for use by any UEs for transmitting a NACKin response to the UEs unable to correctly decode a data packet receivedin a previous transmission. The reservation may be performed, e.g., bythe reservation component 1604 of the apparatus 1600. In one aspect, toaccommodate NACK transmitting UEs without compromising the data rate ofother UEs that do not transmit NACKs in the feedback symbol of theconfigured slot, the first device may fill a first symbol that is onesymbol before the first feedback symbol and a second symbol that is onesymbol after the feedback symbol with the portion of the first packetafter filling the other symbols in the one or more slots. The othersymbols of the aggregation of transmitting slots may be filled with coderate matched data from a buffer. For example, the first device may placedata from the first packet in the other symbols in the one or more slotsbefore placing data in the symbols adjacent to the feedback symbol. Ifadditional data of the first packet remains, the first device may thenplace data in the symbol before the feedback symbol and the symbol afterthe feedback symbol. The first feedback symbol may include symbolthirteen of the first transmitting slot. The first symbol that is onesymbol before the first feedback symbol may be symbol twelve of thefirst transmitting slot, and the second symbol that is one symbol afterthe first feedback symbol may be symbol fourteen of the firsttransmitting slot.

At 1514, the first device may reserve the feedback symbol fortransmitting the NACK to be every N slots, e.g., such as described inconnection with the example in FIG. 8 . The reservation may beperformed, e.g., by the reservation component 1604 of the apparatus1600. In one aspect, dedicated NACK symbols after every N slots may beused for transmitting NACKs for data packets that were unsuccessfullydecode in the previous N slots. The NACKs for the data packettransmitted in the N slots may be multiplexed and transmitted in thededicated NACK symbol. For example, three symbols may be dedicated forNACK. The three symbols may include a first turnaround symbol to allow areceiving UE to switch from the receiving mode to the transmitting mode,a NACK feedback symbol for transmitting the NACK signals, and a secondturnaround symbol to switch from the transmitting mode back to thereceiving mode. In one aspect, N is configurable.

At 1516, the first device may reserve the feedback symbol fortransmitting the NACKS in a configured slot that is a number of slotsafter the start of the current aggregation of transmitting slots or fromthe end of the previous transmission. The reservation may be performed,e.g., by the reservation component 1604 of the apparatus 1600. Thereserved slot may be configurable to allow sufficient time for areceiving device to determine if the data packet is received in errorduring the previous transmission. In one aspect, the reserved slot maybe the first slot of the one or more transmitting slots and the feedbacksymbol may be symbol 13. In one aspect, the reserved slot may be thesecond slot of the one or more transmitting slots and the feedbacksymbol may be symbol 2.

At 1508, the first device may refrain from transmitting the first packetduring the first feedback symbol of the transmitting slot. Thetransmission may be controlled, e.g., by data packet transmissioncontrol component 1608 of the apparatus 1600. In one aspect, theconfigured slot may be configured to be N slots after the end of one ormore transmitting slots during which the first data packet wastransmitted.

At 1510, the first device may listen to NACKs transmitted by any otherUEs during the feedback symbol of the configured slot if the first UEalso transmitted in a previous transmission. The first device may switchto a receiving mode after the one or more slots and may receive a firstNACK from the one or more devices in a second feedback symbol of a slotafter an end of the one or more slots. The first NACK may be received inresponse to the one or more devices receiving the first packetincorrectly during the one or more slots. In some aspects, the slot mayinclude a first slot that follows the one or more slots, and thefeedback symbol may include symbol thirteen of the first slot thatfollows the one or more slots. In some aspects, the slot may include asecond slot that is separated from the one or more slots by at least oneslot, and the feedback symbol may include a second symbol of the slot.The slot may be a configurable number of slots after the one or moreslots. In some aspects, the first device may receive the first NACKduring a receiving portion of the second feedback symbol of the slot.The listening or reception may be performed, e.g., by the NACK feedbackreception component 1614 of the apparatus 1600. For example, a second UEmay transmit a NACK on the feedback symbol of the configured slot torequest the first UE to retransmit a data packet transmitted in theprevious transmission because the second UE was not able to correctlyreceive the data packet in the previous transmission. If the first UEdid not transmit in the previous transmission, the first device mayignore any NACKs received during the feedback symbol of the configuredslot. The first device may resume transmitting the first packet afterthe feedback symbol of the configured slot.

At 1512, the first device may retransmit the data packet transmitted inthe previous transmission if a NACK was received during the feedbacksymbol of the configured slot. The retransmission may be transmitted,e.g., by the data packet transmission control component 1608 and/or thetransmission component 1612 of the apparatus 1600. In one aspect, thefirst device may retransmit the data packet in a subsequent transmissionfollowing the end of the current one or more transmitting slots.

FIG. 16 is a conceptual data flow diagram illustrating the data flowbetween different modules/means/components in an example apparatus 1600in accordance with certain aspects of the disclosure. The apparatus 1600may be a UE or a component of a UE. The apparatus 1600 may include atransmission component 1612, a contention component 1602, a reservationcomponent 1604, a data buffering component 1606, a data packettransmission control component 1608, and a reception component 1610.

The contention component 1602 may be configured to contend for access totransmission resources. For example, the contention component 1602 maybe configured to transmit a LBT sequence during the first symbol of aslot. Other UEs may contend for the transmission resources bytransmitting their LBT sequences. After performing the LBT sequence, theapparatus 1600 may use one transmitting slot or an aggregation oftransmitting slots for transmitting control and a first data packet.

The reservation component 1604 may be configured to reserve a feedbacksymbol of a configured slot for use by any UEs for transmitting a NACKin response to the UEs unable to correctly decode a data packet receivedin a previous transmission. In one aspect, the reservation component1604 may be configured to reserve a feedback symbol of the configuredslot for transmitting the NACK to be every N slots. In one aspect,dedicated NACK symbols after every N slots may be used for transmittingNACKs for data packets that were unsuccessfully decode in the previous Nslots. The NACKs for the data packet transmitted in the N slots may bemultiplexed and transmitted in the dedicated NACK symbol. For example,three symbols may be dedicated for NACK. The three symbols may include afirst turnaround symbol to allow a receiving UE to switch from thereceiving mode to the transmitting mode, a NACK feedback symbol fortransmitting the NACK signals, and a second turnaround symbol to switchfrom the transmitting mode back to the receiving mode. In one aspect, Nis configurable. In one aspect, the reservation component 1604 may beconfigured to reserve a feedback symbol of the configured slot fortransmitting the NACKS to be a number of slots after the start of thecurrent aggregation of transmitting slots or from the end of theprevious transmission. The reserve feedback symbol of the configuredslot may be configurable to allow sufficient time for a receiving deviceto determine if a data packet is received in error during the previoustransmission. In one aspect, the configured slot may be the first slotof the one or more transmitting slots and the feedback symbol may besymbol 13. In one aspect, the configured slot may be the second slot ofthe one or more transmitting slots and the feedback symbol may be symbol2.

The data buffering component 1606 may be configured to buffer the datapacket to be transmitted and to fill the symbols of the transmissionslots with the buffered data packet. In one aspect, to accommodate NACKtransmitting UEs without compromising the data rate of other UEs that donot transmit NACKs in the feedback symbol of the configured slot, thedata buffering component 1606 may be configured to fill the symbolsprior and after the feedback symbols in every slot after all othersymbols in the aggregation of transmitting slots are filled with coderate matched data from a buffer.

The data packet transmission control component 1608 is configured torefrain from transmitting during the feedback symbol of the configuredslot. In one aspect, the configured slot may be configured to be N slotsafter the end of one or more transmitting slots during which the firstdata packet was transmitted.

The NACK feedback reception component 1614 may be configured to listenfor any NACKs transmitted by other UEs during the feedback symbol of theconfigured slot if the apparatus 1600 also transmitted in the previoustransmission. The NACKs transmitted by other UEs may indicate to theapparatus 1600 to retransmit the data packet that was transmitted in theprevious transmission because other UEs were not able to receive thedata packet correctly. The NACK feedback reception component 1614 mayprovide any received NACKs to the data packet transmission controlcomponent 1608.

If the apparatus 1600 was transmitting prior to the feedback symbol ofthe configured slot, the data packet transmission control component 1608may be configured to resume transmitting after the feedback symbol ofthe configured slot. If a NACK was received requesting retransmission ofa data packet transmitted in a previous transmission, the NACK feedbackreception component 1614 may retransmit the data packet in the currenttransmission slots, or in a subsequent aggregation of transmissionslots.

The transmission component 1612 may be configured to transmit thetransport block of the data packets to a second device 1650 such asanother UE. The reception component 1610 may be configured to receivethe NACK on the feedback symbol of the configured slot.

The apparatus may include additional components that perform each of theblocks of the algorithm in the aforementioned flowcharts of FIGS. 11 and15 . As such, each block in the aforementioned flowcharts of FIGS. 11and 15 may be performed by a component and the apparatus may include oneor more of those components. The components may be one or more hardwarecomponents specifically configured to carry out the statedprocesses/algorithm, implemented by a processor configured to performthe stated processes/algorithm, stored within a computer-readable mediumfor implementation by a processor, or some combination thereof.

FIG. 17 is a diagram illustrating an example of a hardwareimplementation 1700 for an apparatus 1600′ of a transmitting UEemploying a processing system 1714 in accordance with certain aspects ofthe disclosure. The processing system 1714 may be implemented with a busarchitecture, represented generally by the bus 1708. The bus 1708 mayinclude any number of interconnecting buses and bridges depending on thespecific application of the processing system 1714 and the overalldesign constraints. The bus 1708 links together various circuitsincluding one or more processors and/or hardware components, representedby the processor 1704, the transceiver 1710, components 1602, 1604,1606, 1608, 1610, 1612, 1614, and the computer-readable medium / memory1706. The bus 1708 may also link various other circuits such as timingsources, peripherals, voltage regulators, and power management circuits,which are well known in the art, and therefore, will not be describedany further.

The processing system 1714 may be coupled to a transceiver 1710. Thetransceiver 1710 is coupled to one or more antennas 1720. Thetransceiver 1710 provides a means for communicating with various otherapparatus over a transmission medium. The transceiver 1710 receives asignal from the one or more antennas 1720, extracts information such asthe NACK on the feedback symbol of the configured slot, and provides theextracted information to the processing system 1714. In addition, thetransceiver 1710 receives information from the processing system 1714,specifically the data packets or the transport block, and based on thereceived information, generates a signal to be applied to the one ormore antennas 1720. The processing system 1714 includes a processor 1704coupled to a computer-readable medium / memory 1706. The processor 1704is responsible for general processing, including the execution ofsoftware stored on the computer-readable medium / memory 1706. Thesoftware, when executed by the processor 1704, causes the processingsystem 1714 to perform the various functions described supra for anyparticular apparatus. The computer-readable medium / memory 1706 mayalso be used for storing data that is manipulated by the processor 1704when executing software. The processing system further includes at leastone of the components 1602, 1604, 1606, 1608, 1610, 1612, and 1614. Thecomponents may be software components running in the processor 1704configured to perform the stated processes/algorithm, resident/stored inthe computer readable medium / memory 1706 for implementation by theprocessor 1704, one or more hardware components specifically configuredto carry out the stated processes/algorithm, one or more hardwarecomponents coupled to the processor 1704, or some combination thereof.The processing system 1714 may be a component of the device 310 or thedevice 350 and may include the memory 376, 360 and/or at least one ofthe TX processor 316, 368, the RX processor 370, 356, and thecontroller/processor 375, 359. Alternately, the processing system maycomprise an entire UE.

In one configuration, the apparatus 1600′ includes means for determiningwhether to contend for access to transmission resources. The means fordetermining whether to contend for access to transmission resources maybe implemented by the contention component 1602. The apparatus 1600′ mayinclude means for configuring and reserving a feedback symbol of aconfigured slot for use by any UEs for transmitting a NACK. The meansfor configuring and reserving a feedback symbol of a configured slot foruse by any UEs for transmitting a NACK may be implemented by thereservation component 1604. The apparatus 1600′ may include means forbuffering the data packet to be transmitted and for filling the symbolsof the transmission slots with the buffered data packet. The means forbuffering the data packet to be transmitted and for filling the symbolsof the transmission slots with the buffered data packet may beimplemented by the data buffering component 1606. The apparatus 1600′may include means for refraining from transmitting during the feedbacksymbol of the configured slot and for resuming transmitting after thefeedback symbol of the configured slot. The means for refraining fromtransmitting during the feedback symbol of the configured slot and forresuming transmitting after the feedback symbol of the configured slotmay be implemented by the data packet transmission control component1608. The apparatus 1600′ may include means for listening and receivingNACKs during the feedback symbol of the configured slots. The means forlistening and receiving NACKs during the feedback symbol of theconfigured slots may be implemented by the NACK feedback receptioncomponent 1614. The aforementioned means may be one or more of theaforementioned components of the apparatus 1600 and/or the processingsystem 1714 of the apparatus 1600′ configured to perform the functionsrecited by the aforementioned means. As described supra, the processingsystem 1714 may include the TX processor 316, 368, the RX processor 370,356, and the controller/processor 375, 359. As such, in oneconfiguration, the aforementioned means may be the TX processor 316,368, the RX processor 370, 356, and the controller/processor 375, 359configured to perform the functions recited by the aforementioned means.

The following examples are illustrative only and aspects thereof may becombined with any of the aspects of the previous discussions and/orembodiments or teachings described herein, without limitation.

Example 1 is a method of wireless communication by a first device,comprising receiving from a second device a first data packet in one ormore receiving slots of a TDD frame that includes a plurality of slots,where a slot includes a plurality of symbols. The method furtherincludes determining whether the first data packet is receivedincorrectly, waiting until the end of the one or more receiving slots,and transmitting to the second device a NACK in a NACK feedback symbolin a configured slot after the end of the one or more receiving slots inresponse to the determination that the first data packet is receivedincorrectly. In Example 2, the method of Example 1 further includes thefirst device receiving a second packet in the configured slot from athird device during a receiving mode, switching from the receiving modeto a transmitting mode during a first turnaround symbol of the pluralityof symbols in the configured slot in order to transmit the first NACK inthe NACK feedback symbol, where the first turnaround symbol comes onesymbol before the NACK feedback symbol, and switching from thetransmitting mode back to the receiving mode during a second turnaroundsymbol of the plurality of symbols of the configured slot, where thesecond turnaround symbol comes one symbol after the NACK feedbacksymbol. In Example 3, the method of any of Examples 1-2 further includesthe first device switching to a transmitting mode to transmit a thirdpacket in a slot following the configured slot after transmitting thefirst NACK in the NACK feedback symbol in the configured slot. InExample 4, the methods of any of Examples 1-3 further includes that theconfigured slot includes the first slot that follows the one or morereceiving slots, the NACK feedback symbol includes symbol thirteen ofthe configured slot, the first turnaround symbol includes symbol twelveof the configured slot, and the second turnaround symbol includes symbolfourteen of the configured slot. In Example 5, the methods of any ofExamples 1-4 further includes that the configured slot includes thesecond slot that is separated from the one or more receiving slots, theNACK feedback symbol includes the second symbol of the configured slotby at least one slot, the first turnaround symbol includes the firstsymbol of the configured slot, and the second turnaround symbolsincludes the third symbol of the configured slot. In Example 6, themethods of any of Examples 1-5 further includes that the configured slotis at a configurable number of slots after the one or more receivingslots. In Example 7, the methods of any of Examples 1-6 further includesthe first device receiving a second packet in the configured slot from athird device during a receiving mode, switching from the receiving modeto a transmitting mode during a first turnaround portion of the NACKfeedback symbol of the configured slot, transmitting the first NACK in atransmitting portion of the NACK feedback symbol of the configured slotduring the transmitting mode, and switching from the transmitting modeback to the receiving mode during a second turnaround portion of theNACK feedback symbol of the configured slot. In Example 8, the methodsof any of Examples 1-7 further includes that the NACK feedback symbolincludes a larger sub-carrier spacing than a sub-carrier spacing ofother symbols in the plurality of slots and the transmitting portion ofthe NACK feedback symbol is less than a symbol length of the NACKfeedback symbol. In Example 9, the methods of any of Examples 1-8further includes the first device receiving one or more additional datapackets in the one or more receiving slots from one or more otherdevices, determining whether one or more of the additional data packetsare received incorrectly to generate one or more additional NACKscorresponding to the one or more additional data packets, andtransmitting to the one or more other devices the one or more additionalNACKs along with the first NACK in the NACK feedback symbol in theconfigured slot in response to the determination that one or more of theadditional data packets are received incorrectly. In Example 10, themethods of any of Examples 1-9 further includes that the number of theone or more receiving slots is configurable for receiving the first datapacket and the one or more additional data packets. In Example 11, themethods of any of Examples 1-10 further includes that the NACK feedbacksymbol includes a symbol every N slots of the TDD frame where the NACKfeedback symbol is dedicated to transmitting the NACK. In Example 12,the methods of any of Examples 1-11 further includes that the NACKincludes one or more additional feedback bits transmitted in the NACKfeedback symbol. In Example 13, the methods of any of Examples 1-12further includes that the one or more additional feedback bits aretransmitted by the first device for a unicast transmission. In Example14, the methods of any of Examples 1-13 further includes that the one ormore additional feedback bits include a reference signal that istransmitted by the first device on one of every N subcarriers of theNACK feedback symbol.

Example 15 is a system or apparatus including means for implementing amethod or realizing an apparatus as in any of Examples 1-14.

Example 16 is a device including one or more processors and one or morememories in electronic communication with the one or more processorsstoring instructions executable by the one or more processors to causethe system or apparatus to implement a method as in any of Examples1-14.

Example 17 is a non-transitory computer readable medium storinginstructions executable by one or more processors to cause the one ormore processors to implement a method as in any of Examples 1-14.

Example 18 is a method of wireless communication by a first device,comprising contending for use of one or more slots of a plurality ofslots of a TDD frame for transmitting, where each slot of the one ormore slots includes a plurality of symbols. The method further includestransmitting at least a portion of a first packet to one or more devicesin one or more transmitting slots, reserving a first feedback symbol ina first transmitting slot of the one or more transmitting slots fortransmission of a NACK from the one or more devices, and refraining fromtransmitting the first packet during the feedback symbol of the firsttransmitting slot. In Example 19, the method of Example 18 furtherincludes the first device identifying a first symbol that comes onesymbol before the first feedback symbol, identifying a second symbolthat comes one symbol after the first feedback symbol, and filling thefirst symbol that is one symbol before the first feedback symbol and thesecond symbol that is one symbol after the first feedback symbol withthe portion of the first packet after filling placing data in the othersymbols in the one or more transmitting slots. In Example 20, the methodof any of Examples 18-19 further includes that the first feedback symbolincludes symbol thirteen of the first transmitting slot, the firstsymbol includes symbol twelve of the first transmitting slot, and thesecond symbol includes symbol fourteen of the first transmitting slot.In Example 21, the method of any of Examples 18-20 further includes thefirst device switching to a receiving mode after the one or moretransmitting slots, and receiving a first NACK from the one or moredevices in a second feedback symbol of a configured slot after the endof the one or more transmitting slots, where the first NACK is receivedin response to the one or more devices receiving the first packetincorrectly during the one or more transmitting slots. In Example 22,the method of any of Examples 18-21 further includes that the configuredslot includes the first slot that follows the one or more transmittingslots, and the second feedback symbol includes symbol thirteen of theconfigured slot. In Example 23, the method of any of Examples 18-22further includes that the configured slot includes the second slot thatis separated from the one or more slots by at least one slot, and thesecond feedback symbol includes the second symbol of the configuredslot. In Example 24, the method of any of Examples 18-23 furtherincludes that the configured slot is at a configurable number of slotsafter the one or more transmitting slots. In Example 25, the method ofany of Examples 18-24 further includes the first device receiving thefirst NACK during a receiving portion of the feedback symbol of theconfigured slot.

Example 26 is a system or apparatus including means for implementing amethod or realizing an apparatus as in any of Examples 18-25.

Example 27 is a device including one or more processors and one or morememories in electronic communication with the one or more processorsstoring instructions executable by the one or more processors to causethe system or apparatus to implement a method as in any of Examples18-25.

Example 28 is a non-transitory computer readable medium storinginstructions executable by one or more processors to cause the one ormore processors to implement a method as in any of Examples 18-25.

Example 29 is a method of wireless communication by a first device,comprising receiving from a second device a first data packet in one ormore receiving slots of a TDD frame that includes a plurality of slots,where a plurality of devices contend for use of the plurality of slotsfor transmission, and where a slot includes a plurality of symbols. Themethod further includes determining whether the first data packet isreceived incorrectly, waiting until a set of dedicated symbols totransmit a NACK, and transmitting to the second device the first NACK ina NACK feedback symbol in the set of dedicated symbols after the end ofthe one or more receiving slots in response to the determination thatthe first data packet is received incorrectly. In Example 30, the methodof Example 29 further includes that the set of dedicated symbolsincludes occurrences that are spaced by a number of slots. In Example31, the method of any of Example 29-30 further includes that eachoccurrence of the set of dedicated symbols includes at least threesymbols. In Example 32, the method of any of Example 29-31 furtherincludes that the set of dedicated symbols is reserved by acommunication system for feedback. In Example 33, the method of any ofExample 29-32 further includes that the set of dedicated symbolsincludes symbols within one of the plurality of slots. In Example 34,the method of any of Example 29-33 further includes that the set ofdedicated symbols includes standalone symbols outside of the pluralityof slots. In Example 35, the method of any of Examples 29-34 furtherincludes that the one or more receiving slots containing the first datapacket for which the NACK is transmitted is offset from the set ofdedicated symbols by one or more offset slots. In Example 36, the methodof any of Examples 29-35 further includes that the one or more offsetslots are configurable.

Example 37 is a system or apparatus including means for implementing amethod or realizing an apparatus as in any of Examples 29-36.

Example 38 is a device including one or more processors and one or morememories in electronic communication with the one or more processorsstoring instructions executable by the one or more processors to causethe system or apparatus to implement a method as in any of Examples29-36.

Example 39 is a non-transitory computer readable medium storinginstructions executable by one or more processors to cause the one ormore processors to implement a method as in any of Examples 19-36.

It is understood that the specific order or hierarchy of blocks in theprocesses / flowcharts disclosed is an illustration of exampleapproaches. Based upon design preferences, it is understood that thespecific order or hierarchy of blocks in the processes / flowcharts maybe rearranged. Further, some blocks may be combined or omitted. Theaccompanying method claims present elements of the various blocks in asample order, and are not meant to be limited to the specific order orhierarchy presented.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” The word “exemplary” is used hereinto mean “serving as an example, instance, or illustration.” Any aspectdescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other aspects. Unless specifically statedotherwise, the term “some” refers to one or more. Combinations such as“at least one of A, B, or C,” “one or more of A, B, or C,” “at least oneof A, B, and C,” “one or more of A, B, and C,” and “A, B, C, or anycombination thereof” include any combination of A, B, and/or C, and mayinclude multiples of A, multiples of B, or multiples of C. Specifically,combinations such as “at least one of A, B, or C,” “one or more of A, B,or C,” “at least one of A, B, and C,” “one or more of A, B, and C,” and“A, B, C, or any combination thereof” may be A only, B only, C only, Aand B, A and C, B and C, or A and B and C, where any such combinationsmay contain one or more member or members of A, B, or C. All structuraland functional equivalents to the elements of the various aspectsdescribed throughout this disclosure that are known or later come to beknown to those of ordinary skill in the art are expressly incorporatedherein by reference and are intended to be encompassed by the claims.Moreover, nothing disclosed herein is intended to be dedicated to thepublic regardless of whether such disclosure is explicitly recited inthe claims. The words “module,” “mechanism,” “element,” “device,” andthe like may not be a substitute for the word “means.” As such, no claimelement is to be construed as a means plus function unless the elementis expressly recited using the phrase “means for.”

What is claimed is:
 1. A method for wireless communication by a firstdevice, comprising: contending for use of one or more slots of a timedivision duplex (TDD) frame for transmitting, wherein each slot of theone or more slots includes a plurality of symbols; transmitting at leasta portion of a first packet in the one or more slots; reserving a firstfeedback symbol in a first transmitting slot of the one or more slotsfor reception of a negative acknowledgement signal (NACK) from one ormore devices; and refraining from transmitting the first packet duringthe first feedback symbol of the first transmitting slot.
 2. The methodof claim 1, further comprising: switching from a transmitting mode to areceiving mode during a first turnaround symbol in order to receive asecond NACK in at least one feedback symbol after the one or more slots,wherein the first turnaround symbol comes one symbol before the at leastone feedback symbol; and receiving the second NACK from the one or moredevices in the at least one feedback symbol in a slot after an end ofthe one or more slots, wherein the second NACK indicates that the one ormore devices received the first packet incorrectly during the one ormore slots.
 3. The method of claim 2, further comprising: switching fromthe receiving mode back to the transmitting mode during a second symbolthat comes one symbol after the at least one feedback symbol; andtransmitting a second data packet in the transmitting mode.
 4. Themethod of claim 3, wherein the at least one feedback symbol comprises atleast one NACK feedback symbol for receiving only NACK feedback.
 5. Themethod of claim 2, wherein transmitting at least the portion of thefirst packet and receiving the second NACK comprises receiving andtransmitting using device-to-device communication.
 6. The method ofclaim 2, wherein the slot comprises a first slot that follows the one ormore slots, and the at least one feedback symbol comprises symbolthirteen of the slot.
 7. The method of claim 2, wherein the slotcomprises a second slot that is separated from the one or more slots byat least one slot, and the at least one feedback symbol comprises asecond symbol of the slot.
 8. The method of claim 2, wherein the slot isat a configurable number of slots after the one or more slots.
 9. Themethod of claim 2, further comprising: receiving the second NACK duringa receiving portion of the at least one feedback symbol of the slot. 10.The method of claim 1, further comprising the first device filling afirst symbol that is one symbol before the first feedback symbol and asecond symbol that is one symbol after the first feedback symbol withthe portion of the first packet after filling other symbols in the oneor more slots.
 11. The method of claim 10, wherein the first feedbacksymbol comprises symbol thirteen of the first transmitting slot, thefirst symbol comprises symbol twelve of the first transmitting slot, andthe second symbol comprises symbol fourteen of the first transmittingslot.
 12. A method for wireless communication by a first device,comprising: receiving from a second device a first data packet in one ormore receiving slots of a time division duplex frame; determiningwhether the first data packet is received incorrectly; waiting until aset of dedicated symbols to transmit a first negative acknowledgementsignal (NACK); and transmitting to the second device the first NACK in aNACK feedback symbol in the set of dedicated symbols after an end of theone or more receiving slots in response to determining that the firstdata packet is received incorrectly.
 13. The method of claim 12, whereinthe set of dedicated symbols comprises occurrences spaced by a number ofslots.
 14. The method of claim 13, wherein each occurrence of the set ofdedicated symbols comprises at least three symbols.
 15. The method ofclaim 12, wherein the set of dedicated symbols is reserved by acommunication system for feedback.
 16. The method of claim 12, whereinthe set of dedicated symbols comprises symbols within one of the one ormore receiving slots.
 17. The method of claim 12, wherein the set ofdedicated symbols comprises standalone symbols outside of the one ormore receiving slots.
 18. The method of claim 12, wherein the one ormore receiving slots containing the first data packet for which the NACKis transmitted is offset from the set of dedicated symbols by one ormore offset slots.
 19. The method of claim 18, wherein the one or moreoffset slots are configurable.
 20. An apparatus for wirelesscommunication by a first device, comprising: memory; and at least oneprocessor coupled to the memory and configured to: contend for use ofone or more slots of a time division duplex (TDD) frame fortransmitting, wherein each slot of the one or more slots includes aplurality of symbols; transmit at least a portion of a first packet inthe one or more slots; reserve a first feedback symbol in a firsttransmitting slot of the one or more slots for reception of a negativeacknowledgement signal (NACK) from one or more devices; and refrain fromtransmitting the first packet during the first feedback symbol of thefirst transmitting slot.
 21. The apparatus of claim 20, wherein the atleast one processor is further configured to: switch from a transmittingmode to a receiving mode during a first turnaround symbol in order toreceive a second NACK in at least one feedback symbol after the one ormore slots, wherein the first turnaround symbol comes one symbol beforethe at least one feedback symbol; and receive the second NACK from theone or more devices in the at least one feedback symbol in a slot afteran end of the one or more slots, wherein the second NACK indicates thatthe one or more devices received the first packet incorrectly during theone or more slots.
 22. The apparatus of claim 21, wherein the at leastone processor is further configured to: switch from the receiving modeback to the transmitting mode during a second symbol that comes onesymbol after the at least one feedback symbol; and transmit a seconddata packet in the transmitting mode.
 23. The apparatus of claim 22,wherein the at least one feedback symbol comprises at least one NACKfeedback symbol for receiving only NACK feedback.
 24. The apparatus ofclaim 21, wherein transmission of at least the portion of the firstpacket and reception the second NACK comprises device-to-devicecommunication.
 25. The apparatus of claim 21, wherein the slot comprisesa first slot that follows the one or more slots, and the at least onefeedback symbol comprises symbol thirteen of the slot.
 26. The apparatusof claim 21, wherein the slot comprises a second slot that is separatedfrom the one or more slots by at least one slot, and the at least onefeedback symbol comprises a second symbol of the slot.
 27. The apparatusof claim 21, wherein the slot is at a configurable number of slots afterthe one or more slots.
 28. The apparatus of claim 21, wherein the atleast one processor is further configured to: receive the second NACKduring a receiving portion of the at least one feedback symbol of theslot.
 29. The apparatus of claim 20, wherein the at least one processoris further configured to: fill a first symbol that is one symbol beforethe first feedback symbol and a second symbol that is one symbol afterthe first feedback symbol with the portion of the first packet afterfilling other symbols in the one or more slots.
 30. The apparatus ofclaim 29, wherein the first feedback symbol comprises symbol thirteen ofthe first transmitting slot, the first symbol comprises symbol twelve ofthe first transmitting slot, and the second symbol comprises symbolfourteen of the first transmitting slot.